Catalytic Enantioselective Synthesis of α-Difunctionalized Cyclic Sulfones

Abstract

As saturated heterocyclic building blocks become increasingly popular in medicinal chemistry and drug discovery programs, expansion of the synthetic toolkit to novel stereofunctionalized heterocycles is a priority. Herein, we report the development of a palladium-catalyzed decarboxylative asymmetric allylic alkylation reaction to access a broad range of enantioenriched α-difunctionalized 5- and 6-membered sulfones from easily accessible racemic starting materials. The allylic alkylation step was found to occur with high levels of enantioselectivity as a result of a palladium-mediated dynamic kinetic resolution of E/Z enolate intermediates. This methodology paves the way to hitherto unexplored stereodefined cyclic sulfones for medicinal chemistry applications.

Introduction

Heterocycles have been and remain to be fundamental building blocks of the majority of small molecule drugs.¹ In order to enhance the developability of lead compounds and examine previously untapped areas of chemical and biological space, saturated heterocycles are becoming increasingly important in medicinal chemistry.² In particular, new asymmetric synthetic methods are sought after to access novel stereofunctionalized heterocycles as high value motifs for drug discovery.³

Saturated cyclic sulfones bearing a tetrasubstituted α-sulfonyl stereogenic center are a principal motif of a number of biologically active compounds (Figure 1). For example, 1 and 2 are a patented ATR kinase inhibitor for cancer chemotherapy⁴ and a matrix metalloproteinase inhibitor as an anti-inflammatory agent,⁵ respectively. Similarly, tazobactam (3) is a very common modified penicillin that is used in the clinic as a β-lactamase inhibitor to combat bacterial resistance,⁶ whereas Waldmann and co-workers have discovered that spirocyclic 4 is a selective and potent Mycobacterium tuberculosis protein tyrosine phosphatase B inhibitor, where the R enantiomer of 4 (IC₅₀ 0.32 mM) was found to be 10 times more active than (S)-4.⁷ As such, the development of new enantioselective approaches to install tetrasubstituted α-sulfonyl stereogenic centers is a pertinent area of research.⁸ To date, only a handful of strategies have been reported for the construction of enantioenriched α-difunctionalized 5-membered sulfones, namely, diastereoselectively by using enantiopure starting materials,⁹ or a chiral auxiliary,¹⁰ enantioselectively by oxidation of 1,3-dithiolanes,¹¹ and cyclization of linear precursors by means of enantioselective organocatalysis,¹² metal catalysis,¹³ and photocatalysis.¹⁴ In addition, there is only one report of an enantioselective entry to α-difunctionalized 6-membered sulfones,¹⁵ utilizing stereoselective oxidation of 1,3-dithianes. To the best of our knowledge, there are no enantioselective methods that would enable the direct α-difunctionalization of cyclic sulfones and construct a tetrasubstituted α-sulfonyl stereogenic center.

Figure 1.

Enantioenriched α-disubstituted cyclic sulfones.

To install the α-sulfonyl stereocenter under mild, base-free conditions, we sought to explore the palladium-catalyzed decarboxylative asymmetric allylic alkylation (DAAA) reaction.¹⁶ Since the first report of the palladium-catalyzed DAAA reaction of ketone enolates with prochiral allylic electrophiles,¹⁷ this process has been most commonly used in the allylation of prochiral cyclic enolates, derived from allyl ester and allyl enol carbonate precursors 5 and 6, respectively (A, Scheme 1).¹⁸ While the cyclic nature of the enolate intermediate typically affords high levels of stereocontrol in the construction of the quaternary stereocenter in 7, the situation is more complex in the allylic alkylation of acyclic enolates: as the geometry of the enolate has an impact on the stereoselectivity of the reaction, the enolate precursor 8 must have a defined alkene geometry to ensure high levels of enantioselectivity in the formation of 9.¹⁹ If a mixture of geometrical isomers of allyl enol carbonate 10 is used or a linear allyl ester substrate 11 affords a mixture of E/Z enolates in situ following decarboxylation,²⁰ then only low levels of enantioselectivity would be expected to result in the formation of 9. Due to the challenges associated with the preparation of geometrically pure allyl enol carbonate starting materials 8, the palladium-catalyzed DAAA reaction of acyclic enolates is less common. Notwithstanding, Murakami and co-workers have been able to obtain 9 with high ee from linear precursors 11 due to coordinating effects in the transition state of alkylation,²¹ whereas Stoltz and co-workers have observed an unusual palladium-mediated dynamic kinetic resolution (DKR) of E/Z enolate intermediates,²² giving 9 with high ee from either allyl enol carbonate 10, irrespective of its alkene geometry, or β-carbonyl ester 11.

Scheme 1. Pd-Catalyzed DAAA of Enolates.

Alongside enolates, α-sulfonyl anions are also known to undergo palladium- and iridium-catalyzed asymmetric allylic alkylation,²³ but these processes focus primarily on the installation of an allylic, rather than α-sulfonyl, stereogenic center. Although Tunge and co-workers successfully developed a stereoretentive palladium-catalyzed decarboxylative allylation of sulfones to give tetrasubstituted α-sulfonyl stereocenters, the use of enantiopure starting materials was required.²⁴ To construct enantioenriched tetrasubstituted α-sulfonyl carbon centers from achiral or racemic starting materials, we developed the first palladium-catalyzed DAAA reaction that affords α-difunctionalized cyclic sulfones, namely, thietane 1,1-dioxides 14, from racemic β-carbonyl sulfones 12.²⁵ Despite the implication of a mixture of E/Z enolates 13, this reaction was found to proceed with high levels of stereoselectivity owing to the aforementioned palladium-mediated DKR of enolates. Herein, we describe the development of the palladium-catalyzed DAAA reaction of racemic 5- and 6-membered sulfones 15–17 in order to access enantioenriched α-difunctionalized sulfolanes 18, thiane 1,1-dioxides 19, and thiomorpholine 1,1-dioxides 20 without the need for pre-formed geometrically pure allyl enol carbonate starting materials.

Results and Discussion

To investigate the palladium-catalyzed DAAA reaction in detail, three substrate classes were prepared in a divergent manner from the following cyclic sulfone scaffolds (Scheme 2): sulfolane (21), thiane 1,1-dioxide (22), and N-Boc thiomorpholine 1,1-dioxide (23). Sulfones 21–23 were appended with an allyl ester moiety in 24–26 in good yields. The reaction of the enolate of 24–26 with either a chloroformate or an acid chloride afforded a range of racemic ester- and ketone-substituted sulfone substrates 15–17.

Scheme 2. Substrate Synthesis.

The optimization of the palladium-catalyzed DAAA reaction began with benzyl-ester-substituted sulfolane substrate 15a (Table 1). When the reactions were run in THF as the solvent at room temperature in the presence of a set of ligands L1–4, PHOX ligand L1 afforded 18a in a racemic form (entry 1), whereas Trost ligands L2 and L3 gave poorly selective reactions (entries 2 and 3). The best result was obtained with (S,S)-ANDEN phenyl Trost ligand L4 (entry 4), installing the tetrasubstituted α-stereogenic center in 18a with 74% ee. Lowering the reaction temperature led to a small increase in selectivity (entry 5). A solvent screen indicated that DMF and acetonitrile were not selective (entries 6 and 7), whereas other solvents, such as toluene (entry 8), ethereal ones (entries 9–11), and chlorinated ones (entries 12 and 13), gave much higher selectivity. The best enantioselectivity of 86% ee was obtained with 1,4-dioxane as the solvent (entry 14), and the reaction was found to go to completion within 2 h (entry 15). Given the high freezing point of 1,4-dioxane, an attempt to lower the temperature of the reaction in a mixture of 1,4-dioxane with THF did not lead to an enhancement of ee.

Table 1. Reaction Optimization.

entrya	solvent	ligand	temp.	time, h	yield, %b	ee, %c
1	THF	L1	rt	24	83	0
2	THF	L2	rt	24	78	11
3	THF	L3	rt	24	61	31
4	THF	L4	rt	24	77	74
5	THF	L4	–20 °C	48	70	77
6	DMF	L4	rt	24	84	–3
7	MeCN	L4	rt	24	84	13
8	toluene	L4	rt	24	68	61
9	MTBE	L4	rt	24	75	63
10	Et2O	L4	rt	24	79	65
11	DME	L4	rt	24	79	74
12	CH2Cl2	L4	rt	24	79	72
13	CHCl3	L4	rt	24	78	78
14	1,4-dioxane	L4	rt	24	88	86
15	1,4-dioxane	L4	rt	2	91	86
16	THF:1,4-dioxane 1:1	L4	–20 °C	48	75	81

^aReaction performed with 15a (0.15 mmol), Pd₂(dba)₃ (3.75 μmol), and ligand (9.75 μmol) in solvent (1.5 mL, 0.1 M).

^bIsolated yield.

^cDetermined by chiral HPLC. THF = tetrahydrofuran; DMF = N,N-dimethylformamide; MTBE = methyl tert-butyl ether; DME = 1,2-dimethoxyethane; rt = room temperature.

Using the optimal reaction conditions, a range of ester- and ketone-substituted cyclic sulfones 15–17 were tested to investigate the scope of this methodology (Scheme 3). Starting with sulfolanes 15, phenyl- and p-methoxyphenyl esters 18b and 18c were isolated with high ee. In addition, an X-ray crystal structure of 18b confirmed the absolute stereochemical configuration of the newly formed tetrasubstituted center,²⁶ which is also in agreement with the stereochemical outcome of allylic alkylation of thietane 1,1-dioxides.²⁵ By extension, the sense of stereoinduction was assumed to be the same for the other cyclic sulfone products. Alkyl esters 18c–g were also obtained with high stereoselectivity, albeit the ee of the smaller methyl ester 18h was lower (69% ee). High selectivity was also maintained in the formation of esters 18i and 18j that are functionalized with a substituted allyl group. Surprisingly, ketone substrates 15k–u were found to be much less reactive than esters, necessitating a higher catalyst loading (5 mol % [Pd₂(dba)₃] and 13 mol % L4), where the higher stability of ketone enolates may potentially result in lower nucleophilicity. Although the ee values of aryl ketone products 18k–m were lower, high enantioselectivity was observed in the formation of products bearing larger alkyl ketone substituents, including secondary alkyl ketones 18n–q and tert-butyl 18r. With decreasing steric hindrance, the selectivity was moderate for primary alkyl ketones 18s and 18t, and very low for small methyl ketone 18u. When the same reaction conditions were applied to thiane 1,1-dioxide substrates 16, ester-substituted products 19a–c were formed with moderate selectivity. However, the allylic alkylation of thiane 1,1-dioxides 16 bearing a ketone side chain was more selective, giving phenyl ketone 19d, p-substituted ketones 19e–h, and heteroaryl ketone product 19i in 76–90% ee. Secondary alkyl ketones 19j–l were also formed with high enantioselectivity. tert-Butyl ketone substrate 16m failed to give 19m due to steric bulk, whereas the much smaller methyl ketone in 19n gave a low ee. Finally, thiomorpholine 1,1-dioxide precursors 17 were found to be even less reactive than sulfolanes 15 and thiane 1,1-dioxides 16, requiring a higher catalyst loading even for ester substrates. The selectivity trend was similar to that of thiane 1,1-dioxide products 19: the ee values of esters 20a and 20b were moderate, whereas aryl and alkyl ketone products 20c and 20d were formed with much improved selectivity.

Scheme 3. Substrate Scope Investigation^,,

Reactions performed on a 0.09–0.29 mmol scale with [Pd₂(dba)₃] (2.5 mol % for esters and 5 mol % for ketones) and (S,S)-L4 (6.5 mol % for esters and 13 mol % for ketones) in 1,4-dioxane (0.1 M).

All yields are of the isolated product after purification by chromatography.

All ee values were determined by chiral HPLC.

Catalyst loading: [Pd₂(dba)₃] (5 mol %) and (S,S)-L4 (13 mol %).

Having observed enantioselective product formation despite the implication of exocyclic enolate intermediates in this DAAA reaction, the impact of the enolate geometry on both the magnitude and the sense of enantioinduction was studied (A, Scheme 4). Geometrically pure allyl enol carbonates (Z)-27 and (E)-27, each of which should give rise to a geometrically pure enolate intermediate immediately after decarboxylation, were subjected to the catalytic reaction conditions. 18q was isolated in 82% ee from (Z)-27 and 71% ee from (E)-27, comprising the R stereochemical configuration of the major enantiomer in both cases. By comparison, β-ketoester 15q also afforded (R)-18q as the major enantiomer in 88% ee. Given that the sense of stereoinduction is the same in all three cases, it is likely that the selectivity in the formation of (R)-18q arises from the selective alkylation of one of the two possible enolates in a dynamic kinetic resolution. For this to be the case, a fast interconversion of enolate intermediates needs to take place. As β-ketoester 15q afforded (R)-18q with an ee (88%) that is closer in magnitude to the ee of (R)-18q derived from (Z)-27 (82%) than the ee of (R)-18q derived from (E)-27 (71%), it is likely that the rate of alkylation of the Z-enolate is faster than that of the E-enolate. As such, the enantioselectivity of allylation is presumably determined both by the rate of enolate isomerization and the steric effects of the enolate substituent in the transition state structure. We then tested how closely the enolate nucleophile and the π-allylpalladium(II) electrophile are associated during the course of the reaction (B, Scheme 4). Using a mixture of ester 15b and deuterium-labeled [D]-15d in addition to the expected products 18b and [D]-18d, the formation of crossover compounds [D]-18b and 18d was also observed. The result of the reaction of ketone precursors 15k and [D]-15l was analogous: a mixture of all four products 18k, [D]-18l, [D]-18k, and 18l was isolated. In light of full crossover, the nucleophile–electrophile ion pair can readily separate at some stage of the mechanism. Finally, to ascertain the implication of a free enolate intermediate, competitive allylation between β-estersulfolane 15b and malonate 28 was probed (C, Scheme 4). Formation of an enolate of 15b by means of decarboxylation in the presence of a malonate should result not only in the expected allylated product 18b but also in the deprotonation and allylation of malonate 28 at least to some extent provided that enolate exchange is fast compared to allylation.^19a1H NMR spectroscopy indicated that full conversion of 15b to 18b took place, whereas allylated 29 was not detected and unreacted malonate 28 was recovered. No allylation of malonate 28 was observed in the presence of β-ketosulfolane substrate 15k either. Such a scenario would arise if a free enolate is not a long-lived intermediate in the reaction due to either a very fast allylic alkylation immediately after decarboxylation or a tight association of the enolate with the allylpalladium(II) electrophile. Given the implication of a palladium-mediated E/Z enolate interconversion prior to alkylation, the latter argument seems more likely. The tightly bound nature of the palladium enolate suggests that crossover must occur prior to decarboxylation.

Scheme 4. Mechanistic Study.

The proposed mechanism of the reaction begins with oxidative addition of the palladium(0) catalyst to allyl ester 15 (Scheme 5). The resulting intermediate 30 is likely to exist as a loosely bound ion pair between a carboxylate and a π-allylpalladium(II) complex that can readily undergo crossover. Subsequent decarboxylation gives rise to a mixture of E- and Z-enolates 31, which are tightly associated with the σ-allylpalladium(II) complex. A fast isomerization of (E)-31 and (Z)-31 then takes place, presumably via a carbon-bound palladium enolate tautomer, and preferential allylic alkylation of (Z)-31 over (E)-31 gives rise to enantioenriched product 18.

Scheme 5. Proposed Catalytic Cycle.

Conclusions

In conclusion, we have developed a palladium-catalyzed decarboxylative asymmetric allylic alkylation reaction of 5- and 6-membered sulfones that paves the way for enantioenriched α-difunctionalized sulfolanes, thiane 1,1-dioxides, and thiomorpholine 1,1-dioxides. The success of this approach in achieving high levels of enantioselectivity relies on the dynamic kinetic resolution of E- and Z-enolate intermediates. This method, therefore, offers clear advantages in terms of operational simplicity in that readily accessible racemic allyl ester starting materials can be used without the requirement for the stereoselective synthesis of geometrically pure allyl enol carbonate substrates. What remains to be explored is whether the palladium-mediated dynamic kinetic resolution of acyclic enolates is more generally applicable in the stereoselective allylation of other heterocyclic and acyclic building blocks. This work is ongoing in our laboratory.

Experimental Section

General Information

Oven-dried glassware was used for all reactions under an argon atmosphere. Dry solvents were obtained from commercial sources or an Innovative Technologies PureSolv solvent drying system. All reagents and solvents were used as supplied. Ligands L1–4 were obtained from commercial sources. Petrol refers to the fraction of petroleum that boils between 40 and 60 °C. Aqueous solutions were saturated unless stated otherwise. Silica gel (40–63 μm particle size) was used for flash column chromatography. Thin-layer chromatography (TLC) was carried out using silica gel 60 F254 aluminum-backed plates. Ultraviolet irradiation (254 nm) and staining with potassium permanganate or acidic ammonium molybdate(VI) solutions as appropriate were used to visualize TLC plates. ¹H NMR spectra were obtained using either a Bruker AVANCE III 400 MHz spectrometer or a Bruker FOURIER 300 MHz spectrometer, in CDCl₃ or DMSO-d₆. ¹³C NMR spectra were recorded on the same spectrometers at 100 or 75 MHz, respectively. For ¹H NMR spectra in CDCl₃ or DMSO-d₆, the residual protic solvent CHCl₃ (δ_H = 7.26 ppm) or the central resonance of the residual protic solvent DMSO-d₅ (δ_H = 2.50 ppm), respectively, was used as the internal reference. For ¹³C NMR spectra in CDCl₃ or DMSO-d₆, the central resonance of CDCl₃ (δ_C = 77.0 ppm) or DMSO-d₆ (δ_C = 39.5 ppm), respectively, was used as the internal reference. Where rotamers were present, NMR data were recorded in DMSO-d₆ at 130 °C. NMR data are reported as follows: chemical shift, δ_H (in parts per million, ppm), (multiplicity, coupling constant, J in Hertz, and number of protons). Couplings are expressed as one, or a combination of the following: s, singlet; d, doublet; t, triplet; q, quartet; quint, quintet; sext, sextet; hept, heptet; and m, multiplet. When coincidental coupling constants were observed in the NMR spectra, the apparent multiplicity of the proton resonance in these cases was reported. 1D nuclear Overhauser effect spectroscopy was used to determine the alkene geometry in (Z)-27 and (E)-27. High-resolution mass spectra (HRMS) were recorded using a Shimadzu LCMS-IT-TOF instrument using ESI or APCI conditions. Infrared spectra were recorded on an Agilent Technologies Cary 630 FTIR spectrometer. Melting points were measured on a Sanyo Gallenkamp capillary melting point apparatus. Enantiomeric excesses were determined by chiral HPLC on a Shimadzu NEXERA X2 UHPLC instrument equipped with a UV detector, using either a Chiralcel OD-H or Chiralpak AD-H column. Optical rotations were measured in CHCl₃ using an AA-65 Automatic Polarimeter.

Synthesis of Sulfones 21–23

Sulfolane (21) was obtained from commercial sources. Thiane 1,1-dioxide (22)²⁷ and N-Boc thiomorpholine 1,1-dioxide (23)²⁸ were prepared according to literature procedures.

Synthesis of Compounds 24–26

Allyl-tetrahydrothiophene-2-carboxylate-1,1-dioxide (24)

A solution of LiHMDS (1 M in THF, 200 mL, 200 mmol) in THF (500 mL) was cooled to −78 °C. A solution of sulfolane (21, 12.06 g, 90 mmol) in THF (10 mL) was added dropwise. The mixture was stirred at −78 °C for 1 h. Allyl chloroformate (11.7 mL, 110 mmol) was added dropwise. The mixture was allowed to warm up to room temperature and was stirred for 15 h. The mixture was quenched with aq. HCl (1 N, 500 mL), and the mixture was extracted with EtOAc (3 × 500 mL). The combined organic phase was washed with water (3 × 1 L), brine (1 L), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 2:1] gave 24 (13.7 g, 67%) as a yellow oil. R_f = 0.21 [petrol:EtOAc 2:1]. ¹H NMR (400 MHz, CDCl₃): δ 5.92 (ddt, J = 17.2, 10.5, 5.9 Hz, 1H), 5.37 (dq, J = 17.2, 1.4 Hz, 1H), 5.27 (dq, J = 10.4, 1.2 Hz, 1H), 4.71 (dq, J = 6.0, 1.5 Hz, 2H), 3.95 (t, J = 7.6 Hz, 1H), 3.18–3.04 (m, 2H), 2.59–2.48 (m, 1H), 2.44–2.29 (m, 2H), 2.22–2.08 (m, 1H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 165.2, 131.1, 119.2, 67.0, 64.6, 51.5, 25.9, 20.3 ppm. IR: ν_max (neat) 2969, 1737 cm^–1. HRMS (ESI) m/z: calcd for C₈H₁₁O₄S [M – H]⁻ 203.0384, found 203.0381.

Allyl-1,1-dioxo-thiane-2-carboxylate (25)

A solution of LiHMDS (1 M in THF, 180 mL, 180 mmol) in THF (450 mL) was cooled to −78 °C. A solution of thiane 1,1-dioxide (22, 9.52 mL, 100 mmol) in THF (10 mL) was added dropwise. The mixture was stirred at −78 °C for 1 h. Allyl chloroformate (11.7 mL, 110 mmol) was added dropwise. The mixture was allowed to warm up to room temperature and was stirred for 15 h. The mixture was quenched with aq. HCl (1 N, 500 mL), and the mixture was extracted with EtOAc (3 × 500 mL). The combined organic phase was washed with brine (1 L), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 3:1–2:1] gave 25 (17.4 g, 89%) as a yellow oil. R_f = 0.17 [petrol:EtOAc 4:1]. ¹H NMR (300 MHz, CDCl₃): δ 5.92 (ddt, J = 17.2, 10.4, 5.8 Hz, 1H), 5.38 (dq, J = 17.2, 1.4 Hz, 1H), 5.29 (dq, J = 10.4, 1.3 Hz, 1H), 4.71 (d, J = 5.0 Hz, 2H), 3.88 (ddd, J = 6.4, 4.7, 2.0 Hz, 1H), 3.43 (ddd, J = 13.6, 8.1, 5.2 Hz, 1H), 3.05–2.94 (m, 1H), 2.40–2.23 (m, 2H), 2.18–2.06 (m, 2H), 1.91 (dtt, J = 17.3, 8.9, 4.2 Hz, 1H), 1.67–1.53 (m, 1H) ppm. ¹³C{¹H} NMR (75 MHz, CDCl₃): δ 165.5, 130.9, 119.4, 66.7, 64.9, 50.9, 27.9, 24.0, 20.7 ppm. IR: ν_max (neat) 2939, 2870, 1731 cm^–1. HRMS (ESI) m/z: calcd for C₉H₁₅O₄S [M + H]⁺ 219.0686, found 219.0677.

2-Allyl-4-tert-butyl-1,1-dioxo-1,4-thiazinane-2,4-dicarboxylate (26)

A solution of N-Boc thiomorpholine 1,1-dioxide (23, 11.75 g, 50 mmol) in THF (200 mL) was cooled to −78 °C. A solution of LiHMDS (1 M in THF, 100 mL, 100 mmol) in THF (50 mL) was added dropwise. The reaction mixture was stirred at −78 °C for 1 h. Allyl chloroformate (5.85 mL, 55 mmol) was added dropwise. The mixture was allowed to warm to room temperature and stirred for 4 h. The reaction was quenched with aq. HCl (1 N, 300 mL). The mixture was extracted with EtOAc (3 × 300 mL), washed with brine (500 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [9:1–4:1 petrol:EtOAc] afforded 26 (14.32 g, 90%) as a colorless solid. R_f = 0.22 [2:1 petrol:EtOAc]. m.p.: 78–80 °C. ¹H NMR (400 MHz, DMSO-d₆, 130 °C): δ 5.94 (ddt, J = 17.3, 10.8, 5.5 Hz, 1H), 5.40 (dq, J = 17.3, 1.6 Hz, 1H), 5.27 (dq, J = 10.6, 1.4 Hz, 1H), 4.70 (dt, J = 5.4, 1.5 Hz, 2H), 4.21 (ddd, J = 5.6, 3.7, 1.8 Hz, 1H), 4.09 (ddd, J = 14.7, 6.2, 1.4 Hz, 1H), 4.01–3.91 (m, 2H), 3.75 (dddd, J = 14.6, 8.4, 3.3, 0.9 Hz, 1H), 3.37 (ddd, J = 14.0, 8.4, 3.6 Hz, 1H), 3.20 (dddd, J = 14.0, 6.9, 3.3, 1.8 Hz, 1H), 1.45 (s, 9H) ppm. ¹³C{¹H} NMR (100 MHz, DMSO-d₆, 130 °C): δ 163.1, 152.5, 130.9, 117.6, 79.9, 65.3, 63.5, 49.8, 44.4, 41.6, 27.3 ppm. IR: ν_max (neat) 2985, 2940, 1736, 1701 cm^–1. HRMS (APCI) m/z: calcd for C₁₃H₂₀O₆S [M – H]⁻ 318.1017, found 318.1009.

Synthesis of Allylic Alkylation Precursors 15–17

2-Allyl-2-benzyldihydrothiophene-2,2(3H)-dicarboxylate-1,1-dioxide (15a)

24 (1.00 g, 4.90 mmol) was dissolved in THF (50 mL). NaHMDS (1 M in THF, 5.39 mL, 5.39 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. Benzyl chloroformate (0.77 mL, 5.39 mmol) was added dropwise, and the solution was stirred for 15 h. The reaction was quenched with aq. HCl (1 N, 50 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (100 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 19:1–4:1] gave 15a (1.16 g, 70%) as a colorless oil. R_f = 0.28 [petrol:EtOAc 4:1]. ¹H NMR (400 MHz, CDCl₃): δ 7.39–7.32 (m, 5H), 5.80 (ddt, J = 17.2, 10.4, 5.7 Hz, 1H), 5.37–5.28 (m, 3H), 5.22 (dq, J = 10.4, 1.2 Hz, 1H), 4.70 (dt, J = 5.8, 1.4 Hz, 2H), 3.33 (t, J = 6.4 Hz, 2H), 2.77–2.71 (m, 2H), 2.30–2.20 (m, 2H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 164.2, 164.0, 134.4, 130.5, 128.6, 128.3, 119.5, 75.0, 68.7, 67.6, 50.3, 30.0, 17.0 ppm. IR: ν_max (neat) 3034, 3017, 2961, 1754, 1724 cm^–1. HRMS (ESI) m/z: calcd for C₁₆H₁₈NaO₆S [M + Na]⁺ 361.0716, found 361.0701.

2-Allyl-2-phenyldihydrothiophene-2,2(3H)-dicarboxylate 1,1-dioxide (15b)

24 (50 mg, 0.25 mmol) was dissolved in THF (2 mL). NaHMDS (1 M in THF, 0.28 mL, 0.28 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. Phenyl chloroformate (35 μL, 0.28 mmol) was added dropwise, and the mixture was stirred for 15 h. The reaction was quenched with aq. HCl (1 N, 10 mL). The mixture was extracted with EtOAc (3 × 10 mL), washed with brine (20 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 9:1–4:1] gave 15b (63 mg, 79%) as a colorless solid. R_f = 0.19 [petrol:EtOAc 4:1]. m.p.: 58–60 °C. ¹H NMR (300 MHz, CDCl₃): δ 7.44–7.36 (m, 2H), 7.31–7.24 (m, 1H), 7.18 (dd, J = 8.6, 1.3 Hz, 2H), 5.97 (ddt, J = 17.2, 10.4, 5.8 Hz, 1H), 5.45 (dq, J = 17.2, 1.5 Hz, 1H), 5.33 (dq, J = 10.5, 1.2 Hz, 1H), 4.84 (dq, J = 5.8, 1.3 Hz, 2H), 3.51–3.32 (m, 2H), 2.99–2.86 (m, 1H), 2.79 (quint, J = 7.5 Hz, 1H), 2.41–2.27 (m, 2H) ppm. ¹³C{¹H} NMR (75 MHz, CDCl₃): δ 164.2, 162.9, 150.3, 130.5, 129.6, 126.7, 121.2, 119.9, 75.0, 67.8, 50.6, 30.2, 17.3 ppm. IR: ν_max (neat) 3017, 2967, 1765, 1735 cm^–1. HRMS (ESI) m/z: calcd for C₁₅H₁₆NaO₆S [M + Na]⁺ 347.0560, found 347.0553.

2-Allyl-2-(4-methoxyphenyl)dihydrothiophene-2,2(3H)-dicarboxylate-1,1-dioxide (15c)

24 (306 mg, 1.5 mmol) was dissolved in THF (10 mL). NaHMDS (1 M in THF, 1.65 mL, 1.65 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. 4-Methoxyphenyl chloroformate (0.245 mL, 1.65 mmol) was added dropwise, and the mixture was stirred for 15 h. The reaction was quenched with aq. HCl (1 N, 10 mL). The mixture was extracted with EtOAc (3 × 20 mL), washed with brine (50 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [petrol:EtOAc 9:1–4:1] gave an inseparable mixture of 24:15c in a 1:2.3 ratio (500 mg, corresponding to 400 mg of pure 15c, 75%) as a clear oil. R_f = 0.11 [petrol:EtOAc 4:1]. ¹H NMR (400 MHz, CDCl₃, resonances due to 15c quoted): δ 7.09 (d, J = 9.0 Hz, 2H), 6.89 (d, J = 9.2 Hz, 2H), 6.02–5.89 (m, 1H), 5.48–5.39 (m, 1H), 5.35–5.29 (m, 1H), 4.82 (dq, J = 5.9, 1.5 Hz, 2H), 3.82–3.76 (m, 3H), 3.47–3.32 (m, 2H), 2.90 (dt, J = 14.0, 7.2 Hz, 1H), 2.78 (dt, J = 14.5, 7.3 Hz, 1H), 2.32 (quint, J = 8.0 Hz, 2H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃, resonances due to 15c quoted): δ 164.2, 163.3, 157.8, 143.8, 130.5, 122.0, 119.8, 114.5, 75.0, 67.7, 55.6, 50.5, 30.2, 17.3 ppm. IR: ν_max (neat) 2974, 3014, 1735 cm^–1. HRMS (ESI) m/z: calcd for C₁₆H₁₈NaO₇S [M + Na]⁺ 377.0665, found 377.0650.

2-Allyl-2-(p-tolyl)dihydrothiophene-2,2(3H)-dicarboxylate-1,1-dioxide (15d)

24 (306 mg, 1.5 mmol) was dissolved in THF (10 mL). NaHMDS (1 M in THF, 1.65 mL, 1.65 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. p-Tolyl chloroformate (0.150 mL, 1.65 mmol) was added dropwise, and the mixture was stirred for 15 h. The reaction was quenched with aq. HCl (1 N, 10 mL). The mixture was extracted with EtOAc (3 × 20 mL), washed with brine (50 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [petrol:EtOAc 4:1] gave 15d (153 mg, 30%) as a pale yellow solid. R_f = 0.17 [petrol:EtOAc 4:1]. m.p.: 58–59 °C. ¹H NMR (400 MHz, CDCl₃): δ 7.18 (d, J = 8.7 Hz, 2H), 7.04 (d, J = 8.6 Hz, 2H), 5.95 (ddt, J = 16.8, 11.1, 5.7 Hz, 1H), 5.44 (dd, J = 17.2, 1.7 Hz, 1H), 5.31 (dt, J = 10.5, 1.1 Hz, 1H), 4.82 (d, J = 5.9 Hz, 2H), 3.45–3.31 (m, 2H), 2.89 (dt, J = 14.2, 7.2 Hz, 1H), 2.77 (dtd, J = 14.7, 7.4, 1.2 Hz, 1H), 2.34 (s, 3H), 2.33–2.24 (m, 2H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 164.1, 163.0, 148.0, 136.3, 130.4, 129.9, 120.7, 119.6, 74.9, 67.6, 50.5, 30.1, 20.8, 17.2 ppm. IR: ν_max (neat) 2976, 3010, 1735 cm^–1. HRMS (ESI) m/z: calcd for C₁₆H₁₈NaO₆S [M + Na]⁺ 361.0716, found 361.0713.

2-((9H-Fluoren-9-yl)methyl)-2-allyldihydrothiophene-2,2(3H)-dicarboxylate-1,1-dioxide (15e)

24 (306 mg, 1.5 mmol) was dissolved in THF (6 mL). LiHMDS (1 M in THF, 1.65 mL, 1.65 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. A solution of Fmoc chloride (427 mg, 1.65 mmol) in THF (4 mL) was added dropwise, and the mixture was stirred for 15 h. The reaction was quenched with aq. HCl (1 N, 10 mL). The mixture was extracted with EtOAc (3 × 20 mL), washed with brine (50 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [petrol:EtOAc 9:1–4:1] gave 15e (377 mg, 59%) as a clear oil. N.B. The analogous reaction of 24 with NaHMDS as the base gave 15e in only 9% yield. R_f = 0.36 [petrol:EtOAc 2:1]. ¹H NMR (400 MHz, CDCl₃): δ 7.76 (dt, J = 7.6, 1.0 Hz, 2H), 7.64 (d, J = 7.4 Hz, 2H), 7.41 (tdd, J = 7.6, 1.6, 1.2 Hz, 2H), 7.33 (qd, J = 7.3, 1.0 Hz, 2H), 5.87 (ddt, J = 17.2, 10.4, 5.8 Hz, 1H), 5.37 (dq, J = 17.2, 1.5 Hz, 1H), 5.24 (dq, J = 10.5, 1.2 Hz, 1H), 4.78 (dd, J = 10.8, 5.8 Hz, 1H), 4.75–4.71 (m, 2H), 4.53 (dd, J = 10.8, 6.7 Hz, 1H), 4.27 (t, J = 6.2 Hz, 1H), 3.21 (ddd, J = 13.2, 8.8, 5.9 Hz, 1H), 3.08 (ddd, J = 13.2, 9.0, 6.5 Hz, 1H), 2.68 (ddd, J = 14.1, 8.8, 6.5 Hz, 1H), 2.44 (ddd, J = 14.5, 8.7, 5.9 Hz, 1H), 2.15 (dtdd, J = 13.4, 8.9, 6.7, 6.0 Hz, 1H), 2.08–1.96 (m, 1H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 164.5, 163.8, 143.4, 142.9, 141.3, 141.3, 130.6, 128.0, 128.0, 127.4, 127.3, 125.1, 125.0, 120.0, 119.9, 119.6, 75.0, 68.5, 67.6, 50.1, 46.6, 29.8, 16.8 ppm. IR: ν_max (neat) 2945, 1731 cm^–1. HRMS (ESI) m/z: calcd for C₂₃H₂₂NaO₆S [M + Na]⁺ 449.1029, found 449.1009.

Diallyl-1,1-dioxo-thiolane-2,2-dicarboxylate (15f)

24 (408 mg, 2.0 mmol) was dissolved in THF (15 mL). NaHMDS (1 M in THF, 2.20 mL, 2.2 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. Allyl chloroformate (0.234 mL, 2.2 mmol) was added dropwise, and the mixture was stirred for 15 h. The reaction was quenched with aq. HCl (1 N, 50 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (150 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 4:1] gave 15f (212 mg, 37%) as a yellow oil. R_f = 0.55 [petrol:EtOAc 1:1]. ¹H NMR (400 MHz, CDCl₃): δ 5.85 (ddt, J = 17.2, 10.5, 5.7 Hz, 2H), 5.33 (dq, J = 17.2, 1.5 Hz, 2H), 5.22 (dq, J = 10.5, 1.2 Hz, 2H), 4.70 (dt, J = 5.7, 1.4 Hz, 4H), 3.32–3.25 (m, 2H), 2.70–2.63 (m, 2H), 2.25–2.15 (m, 2H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 163.7, 130.4, 119.1, 74.8, 67.2, 50.1, 29.8, 16.8 ppm. IR: ν_max (neat) 2953, 1731 cm^–1. HRMS (APCI) m/z: calcd for C₁₂H₁₇O₆S [M + H]⁺ 289.0740, found 289.0726.

2′-Allyl-2′-isobutyl-1,1-dioxo-thiolane-2,2-dicarboxylate (15g)

24 (408 mg, 2.0 mmol) was dissolved in THF (15 mL). NaHMDS (1 M in THF, 2.20 mL, 2.2 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. Isobutyl chloroformate (0.286 mL, 2.2 mmol) was added dropwise, and the mixture was stirred for 15 h. The reaction was quenched with aq. HCl (1 N, 50 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (150 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 4:1] gave 15g (415 mg, 68%) as a yellow oil. R_f = 0.60 [petrol:EtOAc 1:1]. ¹H NMR (400 MHz, CDCl₃): δ 5.82 (ddt, J = 17.2, 10.5, 5.6 Hz, 1H), 5.30 (dq, J = 17.2, 1.5 Hz, 1H), 5.17 (dq, J = 10.5, 1.2 Hz, 1H), 4.65 (ddt, J = 5.4, 3.8, 1.4 Hz, 2H), 3.97 (dd, J = 10.5, 6.5 Hz, 1H), 3.91 (dd, J = 10.5, 6.5 Hz, 1H), 3.26–3.19 (m, 2H), 2.65–2.58 (m, 2H), 2.20–2.11 (m, 2H), 1.90 (hept, J = 6.8 Hz, 1H), 0.85 (d, J = 6.8 Hz, 6H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 163.9, 163.7, 130.4, 118.9, 74.7, 72.6, 67.0, 49.9, 29.7, 27.2, 18.5, 18.5, 16.7 ppm. IR: ν_max (neat) 2961, 2877, 1731 cm^–1. HRMS (APCI) m/z: calcd for C₁₃H₂₀O₆S [M + H]⁺ 305.1053, found 305.1043.

2-Allyl-2-methyldihydrothiophene-2,2(3H)-dicarboxylate 1,1-dioxide (15h)

24 (200 mg, 0.98 mmol) was dissolved in THF (15 mL). NaHMDS (1 M in THF, 1.08 mL, 1.08 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. Methyl chloroformate (0.083 mL, 1.08 mmol) was added dropwise, and the mixture was stirred for 15 h. The reaction was quenched with aq. HCl (1 N, 25 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (150 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 4:1] gave 15h (141 mg, 55%) as a yellow oil. R_f = 0.18 [petrol:EtOAc 4:1]. ¹H NMR (300 MHz, CDCl₃): δ 5.92 (ddt, J = 17.1, 10.4, 5.6 Hz, 1H), 5.39 (dq, J = 17.2, 1.5 Hz, 1H), 5.29 (dq, J = 10.4, 1.3 Hz, 1H), 4.76 (dt, J = 5.6, 1.4 Hz, 2H), 3.88 (s, 3H), 3.41–3.25 (m, 2H), 2.73 (td, J = 7.2, 1.9 Hz, 2H), 2.26 (quint, J = 7.5 Hz, 2H) ppm. ¹³C{¹H} NMR (75 MHz, CDCl₃): δ 164.7, 164.1, 130.6, 119.4, 74.9, 67.5, 53.9, 50.2, 30.0, 17.0 ppm. IR: ν_max (neat) 2957, 1733 cm^–1. HRMS (APCI) m/z: calcd for C₁₀H₁₅O₆S [M + H]⁺ 263.0584, found 263.0577.

(2-Methylallyl)tetrahydrothiophene-2-carboxylate-1,1-dioxide (33)

21 (334 mg, 2.78 mmol) was dissolved in THF (25 mL), and the solution was cooled to −78 °C. LiHMDS (1 M in THF, 5.57 mL, 5.57 mmol) was added dropwise. The mixture was stirred at −78 °C for 1 h. A solution of 32(19c) (500 mg, 3.00 mmol) in THF (5 mL) was added dropwise. The mixture was allowed to warm up to room temperature and stirred for 15 h. The reaction was quenched with aq. HCl (1 N, 25 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (150 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 2:1] gave 33 (485 mg, 80%) as a colorless oil. R_f = 0.32 [petrol:EtOAc 2:1]. ¹H NMR (300 MHz, CDCl₃): δ 5.04 (hept, J = 1.2 Hz, 1H), 4.97 (tt, J = 1.6, 0.8 Hz, 1H), 4.67 (d, J = 12.8 Hz, 1H), 4.60 (d, J = 12.8 Hz, 1H), 3.94 (t, J = 7.6 Hz, 1H), 3.21–3.03 (m, 2H), 2.63–2.48 (m, 1H), 2.47–2.28 (m, 2H), 2.26–2.07 (m, 1H), 1.78 (s, 3H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 165.3, 139.0, 114.3, 69.8, 64.7, 51.5, 26.0, 20.4, 19.4 ppm. IR: ν_max (neat) 3084, 2952, 1735 cm^–1. HRMS (APCI) m/z: calcd for C₉H₁₅O₄S [M + H]⁺ 219.0686, found 219.0676.

2-(2-Methylallyl)-2-phenyldihydrothiophene-2,2(3H)-dicarboxylate-1,1-dioxide (15i)

33 (100 mg, 0.46 mmol) was dissolved in THF (6 mL). NaHMDS (1 M in THF, 0.51 mL, 0.51 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. Phenyl chloroformate (0.064 mL, 0.51 mmol) was added dropwise, and the mixture was stirred for 15 h. The reaction was quenched with aq. HCl (1 N, 5 mL). The mixture was extracted with EtOAc (3 × 10 mL), washed with brine (30 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 4:1] gave 15i (77 mg, 50%) as a colorless oil. R_f = 0.21 [petrol:EtOAc 4:1]. ¹H NMR (400 MHz, CDCl₃): δ 7.43–7.35 (m, 2H), 7.27 (t, J = 7.4 Hz, 1H), 7.17 (d, J = 7.4 Hz, 2H), 5.10 (quint, J = 1.2 Hz, 1H), 5.00 (t, J = 1.6 Hz, 1H), 4.77 (d, J = 12.7 Hz, 1H), 4.72 (d, J = 12.9 Hz, 1H), 3.46–3.32 (m, 2H), 2.91 (dt, J = 15.1, 7.8 Hz, 1H), 2.78 (dt, J = 14.5, 7.4 Hz, 1H), 2.36–2.26 (m, 2H), 1.80 (s, 3H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 164.2, 162.9, 150.2, 138.4, 129.5, 126.6, 121.1, 114.6, 75.0, 70.5, 50.5, 30.2, 19.3, 17.2 ppm. IR: ν_max (neat) 3073, 2956, 1735 cm^–1. HRMS (APCI) m/z: calcd for C₁₆H₁₉O₆S [M + H]⁺ 339.0897, found 339.0895.

2-(2-Methylallyl)-2-(p-tolyl)dihydrothiophene-2,2(3H)-dicarboxylate-1,1-dioxide (15j)

33 (240 mg, 1.10 mmol) was dissolved in THF (10 mL). NaHMDS (1 M in THF, 1.35 mL, 1.35 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. p-Tolyl chloroformate (0.200 mL, 1.35 mmol) was added dropwise, and the mixture was stirred for 15 h. The reaction was quenched with aq. HCl (1 N, 10 mL). The mixture was extracted with EtOAc (3 × 25 mL), washed with brine (50 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 9:1–4:1] gave 15j (213 mg, 55%) as a yellow solid. R_f = 0.30 [petrol:EtOAc 4:1]. m.p.: 70–71 °C. ¹H NMR (400 MHz, CDCl₃): δ 7.18 (d, J = 7.8 Hz, 2H), 7.05 (d, J = 8.7 Hz, 2H), 5.10 (hept, J = 1.2 Hz, 1H), 5.00 (tq, J = 2.4, 1.2 Hz, 1H), 4.77 (dt, J = 12.7, 0.8 Hz, 1H), 4.72 (dt, J = 12.8, 0.9 Hz, 1H), 3.47–3.32 (m, 2H), 2.96–2.86 (m, 1H), 2.79 (dt, J = 14.5, 7.4 Hz, 1H), 2.36–2.28 (m, 5H), 1.80 (s, 3H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 164.2, 163.2, 148.1, 138.5, 136.4, 130.0, 120.8, 114.7, 75.0, 70.5, 50.5, 30.2, 20.9, 19.4, 17.2 ppm. IR: ν_max (neat) 3017, 2970, 2920, 1765, 1730 cm^–1. HRMS (APCI) m/z: calcd for C₁₇H₂₁O₆S [M + H]⁺ 353.1053, found 353.1052.

Allyl-2-benzoyltetrahydrothiophene-2-carboxylate-1,1-dioxide (15k)

24 (1.00 g, 4.90 mmol) was dissolved in THF (50 mL). NaHMDS (1 M in THF, 5.39 mL, 5.39 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. Benzoyl chloride (0.63 mL, 5.39 mmol) was added dropwise, and the mixture was heated at 80 °C for 15 h. The mixture was allowed to cool to room temperature and quenched with aq. HCl (1 N, 50 mL). The mixture was extracted with EtOAc (3 × 100 mL), washed with brine (200 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 9:1–4:1] gave 15k (1.13 g, 75%) as a colorless solid. R_f = 0.18 [petrol:EtOAc 4:1]. m.p.: 81–83 °C. ¹H NMR (400 MHz, CDCl₃): δ 7.97–7.91 (m, 2H), 7.58 (tt, J = 7.4, 1.2 Hz, 1H), 7.46 (tt, J = 7.1, 1.8 Hz, 2H), 5.63 (ddt, J = 17.2, 10.4, 5.9 Hz, 1H), 5.16 (dq, J = 12.9, 1.3 Hz, 1H), 5.13 (dq, J = 6.0, 1.3 Hz, 1H), 4.62 (dt, J = 6.0, 1.3 Hz, 2H), 3.49–3.33 (m, 2H), 3.14 (dt, J = 14.7, 7.5 Hz, 1H), 2.72 (ddd, J = 14.2, 7.5, 6.4 Hz, 1H), 2.40–2.19 (m, 2H) ppm. ¹³C{¹H} NMR (75 MHz, CDCl₃): δ 188.2, 166.0, 135.3, 133.8, 130.1, 129.0, 128.6, 120.0, 77.8, 67.3, 51.8, 31.9, 17.6 ppm. IR: ν_max (neat) 3066, 2954, 1735, 1685 cm^–1. HRMS (ESI) m/z: calcd for C₁₅H₁₆NaO₅S [M + Na]⁺ 331.0611, found 331.0597.

Allyl-2-(p-toluoyl)tetrahydrothiophene-2-carboxylate-1,1-dioxide (15l)

24 (100 mg, 0.49 mmol) was dissolved in THF (6 mL). NaHMDS (1 M in THF, 0.54 mL, 0.54 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. p-Toluoyl chloride (0.071 mL, 0.54 mmol) was added dropwise, and the mixture was heated at 80 °C for 15 h. The mixture was allowed to cool to room temperature and quenched with aq. HCl (1 N, 5 mL). The mixture was extracted with EtOAc (3 × 10 mL), washed with brine (30 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 4:1] gave 15l (79 mg, 50%) as a colorless solid. R_f = 0.14 [petrol:EtOAc 4:1]. m.p.: 64–66 °C. ¹H NMR (400 MHz, CDCl₃): δ 7.83 (d, J = 8.4 Hz, 2H), 7.24 (d, J = 8.1 Hz, 2H), 5.65 (ddt, J = 17.3, 10.4, 5.9 Hz, 1H), 5.20–5.09 (m, 2H), 4.61 (dt, J = 5.9, 1.3 Hz, 2H), 3.46–3.28 (m, 2H), 3.11 (dt, J = 14.7, 7.5 Hz, 1H), 2.67 (ddd, J = 14.2, 7.5, 6.4 Hz, 1H), 2.38 (s, 3H), 2.33–2.16 (m, 2H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 187.4, 166.1, 144.8, 132.7, 130.1, 129.3, 129.1, 119.7, 77.6, 67.1, 51.7, 31.8, 21.6, 17.5 ppm. IR: ν_max (neat) 3076, 3022, 2993, 1739, 1679 cm^–1. HRMS (ESI) m/z: calcd for C₁₆H₁₉O₅S [M + H]⁺ 323.0948, found 323.0944.

Allyl-2-(furan-2-carbonyl)-1,1-dioxo-thiolane-2-carboxylate (15m)

24 (408 mg, 2.0 mmol) was dissolved in THF (15 mL). NaHMDS (1 M in THF, 2.20 mL, 2.2 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. 2-Furoyl chloride (0.217 mL, 2.2 mmol) was added dropwise, and the mixture was heated at 80 °C for 15 h. The mixture was allowed to cool to room temperature and quenched with aq. HCl (1 N, 25 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (150 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 6:1–4:1] gave an inseparable mixture of starting material 24 and 15m in a 1:5.2 ratio (491 mg, corresponding to 434 mg of pure 15m, 73%) as a yellow oil. R_f = 0.61 [petrol:EtOAc 1:1]. ¹H NMR (400 MHz, CDCl₃, resonances due to 15m quoted): δ 7.55 (dd, J = 1.6, 0.6 Hz, 1H), 7.29 (dd, J = 3.7, 0.6 Hz, 1H), 6.49 (dd, J = 3.7, 1.7 Hz, 1H), 5.66 (ddt, J = 17.3, 10.5, 5.8 Hz, 1H), 5.16–5.07 (m, 2H), 4.58 (tt, J = 6.0, 1.3 Hz, 2H), 3.33–3.18 (m, 2H), 2.98 (dt, J = 14.2, 7.2 Hz, 1H), 2.52 (dt, J = 14.4, 7.3 Hz, 1H), 2.26–2.16 (m, 1H), 2.13–2.04 (m, 1H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃, resonances due to 15m quoted): δ 175.5, 165.0, 150.5, 147.2, 130.2, 119.7, 119.2, 112.6, 76.6, 66.8, 51.6, 30.3, 17.3 ppm. IR: ν_max (neat) 3136, 2953, 1735, 1671 cm^–1. HRMS (APCI) m/z: calcd for C₁₃H₁₅O₆S [M + H]⁺ 299.0584, found 299.0578.

Allyl-2-(cyclohexanecarbonyl)-1,1-dioxo-thiolane-2-carboxylate (15n)

24 (408 mg, 2.0 mmol) was dissolved in THF (15 mL). NaHMDS (1 M in THF, 2.20 mL, 2.2 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. Cyclohexanecarbonyl chloride (0.294 mL, 2.2 mmol) was added dropwise, and the mixture was heated at 80 °C for 15 h. The mixture was allowed to cool to room temperature and quenched with aq. HCl (1 N, 25 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (150 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 9:1–4:1] gave 15n (444 mg, 71%) as a yellow solid. R_f = 0.71 [petrol:EtOAc 1:1]. m.p.: 54–56 °C. ¹H NMR (400 MHz, CDCl₃): δ 5.94 (ddt, J = 17.1, 10.4, 6.1 Hz, 1H), 5.42 (dq, J = 17.2, 1.4 Hz, 1H), 5.32 (dq, J = 10.4, 1.1 Hz, 1H), 4.76 (dt, J = 6.0, 1.0 Hz, 2H), 3.30–3.13 (m, 2H), 3.04–2.95 (m, 1H), 2.72 (dt, J = 14.7, 7.6 Hz, 1H), 2.57 (dt, J = 14.4, 7.4 Hz, 1H), 2.21–2.11 (m, 2H), 2.03–1.92 (m, 1H), 1.80–1.69 (m, 3H), 1.65 (ddd, J = 7.6, 3.8, 2.3 Hz, 1H), 1.45–1.33 (m, 1H), 1.31–1.16 (m, 4H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 202.0, 164.5, 130.4, 120.5, 80.0, 67.6, 50.7, 49.6, 30.5, 28.9, 28.8, 25.5, 25.1, 16.9 ppm. IR: ν_max (neat) 2931, 2855, 1735, 1705 cm^–1. HRMS (APCI) m/z: calcd for C₁₅H₂₃O₅S [M + H]⁺ 315.1261, found 315.1255.

Allyl-1,1-dioxo-2-(tetrahydropyran-4-carbonyl)thiolane-2-carboxylate (15o)

24 (408 mg, 2.0 mmol) was dissolved in THF (15 mL). NaHMDS (1 M in THF, 2.20 mL, 2.2 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. Tetrahydro-2H-pyran-4-carbonyl chloride (327 mg, 2.2 mmol) was added, and the mixture was heated at 80 °C for 15 h. The mixture was allowed to cool to room temperature and quenched with aq. HCl (1 N, 25 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (150 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 6:1–4:1] gave an inseparable mixture of starting material 24 and 15o in a 1:3.4 ratio (443 mg, corresponding to 372 mg of pure 15o, 59%) as a colorless solid. R_f = 0.52 [petrol:EtOAc 1:1]. m.p.: 59–61 °C. ¹H NMR (400 MHz, CDCl₃, resonances due to 15o quoted): δ 5.95 (ddt, J = 17.0, 10.4, 6.1 Hz, 1H), 5.43 (dq, J = 17.2, 1.4 Hz, 1H), 5.35 (dq, J = 10.4, 1.1 Hz, 1H), 4.77 (dt, J = 6.1, 1.2 Hz, 2H), 4.02–3.93 (m, 2H), 3.50–3.25 (m, 4H), 3.20 (ddd, J = 13.1, 8.4, 6.3 Hz, 1H), 2.84 (ddd, J = 14.8, 8.3, 6.9 Hz, 1H), 2.56 (ddd, J = 14.3, 8.0, 6.4 Hz, 1H), 2.30–2.12 (m, 2H), 1.93 (dtd, J = 13.4, 3.6, 1.6 Hz, 1H), 1.86–1.65 (m, 3H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃, resonances due to 15o quoted): δ 199.8, 164.3, 130.1, 120.2, 79.8, 67.3, 66.5, 66.4, 50.8, 46.6, 29.9, 28.6, 28.5, 16.9 ppm. IR: ν_max (neat) 2957, 2845, 1735, 1716 cm^–1. HRMS (APCI) m/z: calcd for C₁₄H₂₁O₆S [M + H]⁺ 317.1053, found 317.1038.

Allyl-2-(cyclopropanecarbonyl)-1,1-dioxo-thiolane-2-carboxylate (15p)

24 (408 mg, 2.0 mmol) was dissolved in THF (15 mL). NaHMDS (1 M in THF, 2.20 mL, 2.2 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. Cyclopropanecarbonyl chloride (0.200 mL, 2.2 mmol) was added dropwise, and the mixture was heated at 80 °C for 15 h. The mixture was allowed to cool to room temperature and quenched with aq. HCl (1 N, 25 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (150 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 4:1] gave 15p (444 mg, 82%) as a colorless oil. R_f = 0.59 [petrol:EtOAc 1:1]. ¹H NMR (400 MHz, CDCl₃): δ 5.83 (ddt, J = 17.1, 10.5, 5.8 Hz, 1H), 5.29 (dq, J = 17.2, 1.4 Hz, 1H), 5.19 (dq, J = 10.5, 1.2 Hz, 1H), 4.66 (ddt, J = 5.6, 2.7, 1.3 Hz, 2H), 3.25 (ddd, J = 13.1, 8.9, 7.4 Hz, 1H), 3.12 (ddd, J = 14.0, 8.4, 5.6 Hz, 1H), 2.72 (ddd, J = 14.6, 8.2, 6.6 Hz, 1H), 2.42 (ddd, J = 14.5, 8.1, 6.6 Hz, 1H), 2.36–2.29 (m, 1H), 2.21–2.09 (m, 1H), 2.09–1.97 (m, 1H), 1.11–1.01 (m, 2H), 1.01–0.92 (m, 2H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 197.5, 164.6, 130.3, 119.3, 79.5, 67.0, 50.8, 28.2, 20.9, 16.9, 13.5, 13.4 ppm. IR: ν_max (neat) 2955, 1735, 1701 cm^–1. HRMS (APCI) m/z: calcd for C₁₂H₁₇O₅S [M + H]⁺ 273.0791, found 273.0783.

Allyl-2-(2-methylpropanoyl)-1,1-dioxo-thiolane-2-carboxylate (15q)

24 (250 mg, 1.12 mmol) was dissolved in THF (20 mL). NaHMDS (1 M in THF, 1.35 mL, 1.35 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. Isobutyryl chloride (0.140 mL, 1.35 mmol) was added dropwise, and the mixture was heated at 80 °C for 15 h. The mixture was allowed to cool to room temperature and quenched with aq. HCl (1 N, 25 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (150 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 4:1] gave 15q (184 mg, 60%) as a yellow oil. R_f = 0.33 [petrol:EtOAc 4:1]. ¹H NMR (400 MHz, CDCl₃) δ 5.96 (ddt, J = 17.2, 10.4, 6.0 Hz, 1H), 5.43 (dq, J = 17.1, 1.4 Hz, 1H), 5.34 (dq, J = 10.4, 1.1 Hz, 1H), 4.78 (dt, J = 6.0, 1.2 Hz, 2H), 3.37–3.17 (m, 3H), 2.81–2.71 (m, 1H), 2.61 (dt, J = 14.4, 7.4 Hz, 1H), 2.24–2.15 (m, 2H), 1.19 (d, J = 6.5 Hz, 3H), 1.12 (d, J = 6.7 Hz, 3H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 203.5, 164.6, 130.4, 120.5, 80.1, 67.7, 50.7, 39.6, 28.9, 20.4, 19.4, 17.0 ppm. IR: ν_max (neat) 2978, 2877, 1735, 1718 cm^–1. HRMS (APCI) m/z: calcd for C₁₂H₁₉O₅S [M + H]⁺ 275.0948, found 275.0943.

Allyl-2-(2,2-dimethylpropanoyl)-1,1-dioxo-thiolane-2-carboxylate (15r)

24 (408 mg, 2.0 mmol) was dissolved in THF (15 mL). NaHMDS (1 M in THF, 2.20 mL, 2.2 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. Pivaloyl chloride (0.271 mL, 2.2 mmol) was added dropwise, and the mixture was heated at 80 °C for 15 h. The mixture was allowed to cool to room temperature and quenched with aq. HCl (1 N, 25 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (150 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 9:1–4:1] gave 15r (118 mg, 20%) as a yellow oil. R_f = 0.63 [petrol:EtOAc 1:1]. ¹H NMR (400 MHz, CDCl₃) δ 5.89 (ddt, J = 16.5, 10.4, 6.1 Hz, 1H), 5.38 (dq, J = 17.2, 1.3 Hz, 1H), 5.28 (dd, J = 10.4, 1.0 Hz, 1H), 4.75–4.64 (m, 2H), 3.31–3.17 (m, 2H), 2.81 (dt, J = 14.8, 7.6 Hz, 1H), 2.50 (ddd, J = 14.2, 7.6, 6.4 Hz, 1H), 2.22–2.03 (m, 2H), 1.22 (s, 9H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 203.3, 165.3, 130.1, 120.5, 79.0, 67.3, 50.9, 46.1, 31.4, 27.8, 17.0 ppm. IR: ν_max (neat) 2963, 1703 cm^–1. HRMS (APCI) m/z: calcd for C₁₃H₂₁O₅S [M + H]⁺ 289.1104, found 289.1099.

Allyl-2-(3-methylbutanoyl)-1,1-dioxo-thiolane-2-carboxylate (15s)

24 (408 mg, 2.0 mmol) was dissolved in THF (15 mL). NaHMDS (1 M in THF, 2.20 mL, 2.2 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. Isovaleryl chloride (0.268 mL, 2.2 mmol) was added dropwise, and the mixture was heated at 80 °C for 15 h. The mixture was allowed to cool to room temperature and quenched with aq. HCl (1 N, 25 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (150 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 6:1] gave 15s (384 mg, 67%) as a yellow oil. R_f = 0.70 [petrol:EtOAc 1:1]. ¹H NMR (400 MHz, CDCl₃) δ 5.84 (ddt, J = 17.1, 10.4, 5.9 Hz, 1H), 5.32 (dq, J = 17.2, 1.4 Hz, 1H), 5.23 (dq, J = 10.4, 1.1 Hz, 1H), 4.67 (dt, J = 6.0, 1.3 Hz, 2H), 3.24 (ddd, J = 13.2, 8.9, 6.8 Hz, 1H), 3.13 (ddd, J = 13.2, 8.6, 6.3 Hz, 1H), 2.74–2.55 (m, 3H), 2.45 (ddd, J = 14.5, 8.3, 6.2 Hz, 1H), 2.19–2.02 (m, 3H), 0.85 (d, J = 6.7 Hz, 3H), 0.82 (d, J = 6.7 Hz, 3H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 197.0, 164.6, 130.2, 119.9, 79.4, 67.2, 50.5, 49.7, 28.4, 23.7, 22.0, 22.0, 16.7 ppm. IR: ν_max (neat) 2959, 2873, 1735, 1718 cm^–1. HRMS (APCI) m/z: calcd for C₁₃H₂₀NaO₅S [M + Na]⁺ 311.0924, found 311.0916.

Allyl-2-butanoyl-1,1-dioxo-thiolane-2-carboxylate (15t)

24 (408 mg, 2.0 mmol) was dissolved in THF (15 mL). NaHMDS (1 M in THF, 2.20 mL, 2.2 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. Butyryl chloride (0.228 mL, 2.2 mmol) was added dropwise, and the mixture was heated at 80 °C for 15 h. The mixture was allowed to cool to room temperature and quenched with aq. HCl (1 N, 25 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (150 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 6:1] gave 15t (265 mg, 48%) as a colorless oil. R_f = 0.68 [petrol:EtOAc 1:1]. ¹H NMR (400 MHz, CDCl₃) δ 5.86 (ddt, J = 17.1, 10.4, 5.9 Hz, 1H), 5.33 (dq, J = 17.2, 1.4 Hz, 1H), 5.24 (dq, J = 10.4, 1.1 Hz, 1H), 4.68 (dq, J = 6.0, 1.0 Hz, 2H), 3.25 (ddd, J = 13.1, 8.8, 7.1 Hz, 1H), 3.14 (ddd, J = 13.2, 8.5, 6.1 Hz, 1H), 2.82–2.64 (m, 3H), 2.46 (ddd, J = 14.4, 8.2, 6.3 Hz, 1H), 2.22–2.05 (m, 2H), 1.58 (sext d, J = 7.6, 1.1 Hz, 2H), 0.85 (t, J = 7.4 Hz, 3H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 197.7, 164.8, 130.2, 119.9, 79.4, 67.2, 50.7, 43.2, 28.5, 17.0, 16.9, 13.1 ppm. IR: ν_max (neat) 2965, 2877, 1718 cm^–1. HRMS (APCI) m/z: calcd for C₁₂H₁₉O₅S [M + H]⁺ 275.0948, found 275.0939.

Allyl-2-acetyltetrahydrothiophene-2-carboxylate-1,1-dioxide (15u)

24 (200 mg, 0.98 mmol) was dissolved in THF (15 mL). NaHMDS (1 M in THF, 1.08 mL, 1.08 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. Acetyl chloride (0.077 mL, 1.08 mmol) was added dropwise, and the mixture was heated at 80 °C for 15 h. The mixture was allowed to cool to room temperature and quenched with aq. HCl (1 N, 10 mL). The mixture was extracted with EtOAc (3 × 25 mL), washed with brine (50 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 9:1–4:1] gave 15u (121 mg, 50%) as a yellow oil. R_f = 0.26 [petrol:EtOAc 4:1]. ¹H NMR (300 MHz, CDCl₃) δ 5.91 (ddt, J = 17.2, 10.4, 5.9 Hz, 1H), 5.38 (dq, J = 17.2, 1.4 Hz, 1H), 5.31 (dq, J = 10.4, 1.2 Hz, 1H), 4.74 (dq, J = 6.0, 1.2 Hz, 2H), 3.39–3.13 (m, 2H), 2.81 (ddd, J = 14.4, 8.3, 6.6 Hz, 1H), 2.58–2.45 (m, 4H), 2.33–2.06 (m, 2H) ppm. ¹³C{¹H} NMR (75 MHz, CDCl₃): δ 195.3, 164.8, 130.3, 120.1, 79.8, 67.6, 51.1, 29.3, 28.6, 17.3 ppm. IR: ν_max (neat) 2956, 1718 cm^–1. HRMS (APCI) m/z: calcd for C₁₀H₁₅O₅S [M + H]⁺ 247.0635, found 247.0625.

2-Allyl-2-phenyl-1,1-dioxo-thiane-2,2-dicarboxylate (16a)

25 (300 mg, 1.37 mmol) was dissolved in THF (20 mL). NaHMDS (1 M in THF, 1.51 mL, 1.51 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. Phenyl chloroformate (0.190 mL, 1.51 mmol) was added dropwise, and the mixture was stirred for 15 h. The reaction was quenched with aq. HCl (1 N, 25 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (150 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 4:1] gave 16a (195 mg, 43%) as a yellow oil. R_f = 0.22 [petrol:EtOAc 4:1]. ¹H NMR (400 MHz, CDCl₃) δ 7.41 (t, J = 7.9 Hz, 2H), 7.28 (t, J = 7.4 Hz, 1H), 7.14 (d, J = 7.8 Hz, 2H), 5.97 (ddt, J = 16.4, 10.5, 5.7 Hz, 1H), 5.45 (dq, J = 17.2, 1.6 Hz, 1H), 5.33 (dd, J = 10.5, 1.3 Hz, 1H), 4.85 (dd, J = 5.7, 1.6 Hz, 2H), 3.57 (dt, J = 13.7, 6.3 Hz, 1H), 3.50–3.39 (m, 1H), 2.67 (q, J = 6.2, 5.7 Hz, 2H), 2.13 (quint, J = 6.1 Hz, 2H), 1.78 (quint, J = 5.8 Hz, 2H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 163.6, 162.7, 150.1, 130.4, 129.6, 126.7, 121.1, 120.0, 76.5, 67.6, 52.0, 32.5, 24.0, 19.9 ppm. IR: ν_max (neat) 3017, 2985, 2946, 2872, 1767, 1737 cm^–1. HRMS (APCI) m/z: calcd for C₁₆H₁₉O₆S [M + H]⁺ 339.0897, found 339.0884.

2-Allyl-2′-(4-methoxyphenyl)-1,1-dioxo-thiane-2,2-dicarboxylate (16b)

25 (436 mg, 2.0 mmol) was dissolved in THF (15 mL). NaHMDS (1 M in THF, 2.20 mL, 2.2 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. 4-Methoxyphenyl chloroformate (0.327 mL, 2.2 mmol) was added dropwise, and the mixture was stirred for 15 h. The reaction was quenched with aq. HCl (1 N, 25 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (150 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 3:1] gave an inseparable mixture of starting material 25 and 16b in a 1:3.9 ratio (569 mg, corresponding to 494 mg of pure 16b, 67%) as a colorless solid. R_f = 0.55 [petrol:EtOAc 1:1]. m.p.: 67–69 °C. ¹H NMR (400 MHz, CDCl₃) δ 6.94 (d, J = 9.1 Hz, 2H), 6.79 (d, J = 9.1 Hz, 2H), 5.85 (ddt, J = 17.1, 10.6, 5.6 Hz, 1H), 5.33 (dq, J = 17.3, 1.4 Hz, 1H), 5.20 (dq, J = 10.5, 1.3 Hz, 1H), 4.72 (ddt, J = 6.0, 3.2, 1.3 Hz, 2H), 3.65 (s, 3H), 3.42 (dt, J = 13.3, 6.3 Hz, 1H), 3.34–3.24 (m, 1H), 2.61–2.44 (m, 2H), 2.03–1.89 (m, 2H), 1.68–1.57 (m, 2H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 163.1, 162.6, 157.3, 143.0, 130.2, 121.4, 119.1, 114.0, 76.0, 67.0, 55.1, 51.5, 32.0, 23.5, 19.3 ppm. IR: ν_max (neat) 2944, 2838, 1735, 1321, 1129 cm^–1. HRMS (ESI) m/z: calcd for C₁₇H₂₀NaO₇S [M + Na]⁺ 391.0822, found 391.0832.

2-Allyl-2-benzyl-1,1-dioxo-thiane-2,2-dicarboxylate (16c)

25 (436 mg, 2.0 mmol) was dissolved in THF (15 mL). NaHMDS (1 M in THF, 2.20 mL, 2.2 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. Benzyl chloroformate (0.314 mL, 2.2 mmol) was added dropwise, and the mixture was stirred for 15 h. The reaction was quenched with aq. HCl (1 N, 25 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (150 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 4:1] gave 16c (417 mg, 59%) as a colorless oil. R_f = 0.45 [petrol:EtOAc 1:1]. ¹H NMR (400 MHz, CDCl₃) δ 7.38–7.31 (m, 5H), 5.75 (ddt, J = 17.2, 10.5, 5.7 Hz, 1H), 5.35–5.26 (m, 3H), 5.20 (dq, J = 10.4, 1.2 Hz, 1H), 4.67 (dq, J = 5.7, 1.3 Hz, 2H), 3.43 (t, J = 6.2 Hz, 2H), 2.58–2.50 (m, 2H), 2.07 (quint, J = 6.1 Hz, 2H), 1.70–1.61 (m, 2H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 163.8, 163.5, 134.4, 130.4, 128.6, 128.6, 128.2, 119.5, 76.4, 68.5, 67.4, 51.8, 32.4, 23.9, 19.8 ppm. IR: ν_max (neat) 2935, 1731 cm^–1. HRMS (ESI) m/z: calcd for C₁₇H₂₀NaO₆S [M + Na]⁺ 375.0873, found 375.0868.

Allyl-2-benzoyl-1,1-dioxo-thiane-2-carboxylate (16d)

25 (436 mg, 2.0 mmol) was dissolved in THF (15 mL). NaHMDS (1 M in THF, 2.20 mL, 2.2 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. Benzoyl chloride (0.256 mL, 2.2 mmol) was added dropwise, and the mixture was heated at 80 °C for 15 h. The mixture was allowed to cool to room temperature and quenched with aq. HCl (1 N, 25 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (150 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 4:1] gave 16d (521 mg, 81%) as a colorless oil. R_f = 0.65 [petrol:EtOAc 1:1]. ¹H NMR (400 MHz, CDCl₃) δ 7.89 (dd, J = 8.5, 1.2 Hz, 2H), 7.50 (tt, J = 7.4, 1.2 Hz, 1H), 7.36 (t, J = 7.4 Hz, 2H), 5.53 (ddt, J = 17.1, 10.4, 5.9 Hz, 1H), 5.10 (dq, J = 17.2, 1.4 Hz, 1H), 5.05 (dq, J = 10.4, 1.1 Hz, 1H), 4.55 (dq, J = 5.9, 1.1 Hz, 2H), 3.53 (dt, J = 13.5, 6.6 Hz, 1H), 3.48–3.37 (m, 1H), 2.80 (ddd, J = 15.1, 9.7, 3.2 Hz, 1H), 2.58 (ddd, J = 15.1, 7.9, 2.9 Hz, 1H), 2.03 (quint, J = 6.2 Hz, 2H), 1.67–1.49 (m, 2H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 187.9, 165.5, 134.9, 133.5, 129.7, 129.0, 128.2, 119.6, 80.0, 67.0, 52.4, 32.9, 23.6, 19.3 ppm. IR: ν_max (neat) 2937, 2868, 1735, 1679 cm^–1. HRMS (APCI) m/z: calcd for C₁₆H₁₈NaO₅S [M + Na]⁺ 345.0767, found 345.0756.

Allyl-2-(4-bromobenzoyl)-1,1-dioxo-thiane-2-carboxylate (16e)

25 (436 mg, 2.0 mmol) was dissolved in THF (15 mL). NaHMDS (1 M in THF, 2.20 mL, 2.2 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. 4-Bromobenzoyl chloride (483 mg, 2.2 mmol) was added, and the mixture was heated at 80 °C for 15 h. The mixture was allowed to cool to room temperature and quenched with aq. HCl (1 N, 25 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (150 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 4:1] gave 16e (615 mg, 77%) as a colorless solid. R_f = 0.65 [petrol:EtOAc 1:1]. m.p.: 83–85 °C. ¹H NMR (400 MHz, CDCl₃) δ 7.79 (d, J = 8.8 Hz, 2H), 7.52 (d, J = 8.8 Hz, 2H), 5.57 (ddt, J = 17.1, 10.4, 6.0 Hz, 1H), 5.17–5.06 (m, 2H), 4.56 (ddt, J = 6.0, 2.6, 1.2 Hz, 2H), 3.60 (dt, J = 14.4, 7.1 Hz, 1H), 3.35 (dt, J = 13.9, 5.0 Hz, 1H), 2.79 (ddd, J = 14.5, 11.0, 3.0 Hz, 1H), 2.50 (ddd, J = 15.0, 6.9, 2.5 Hz, 1H), 2.08–1.98 (m, 2H), 1.72–1.62 (m, 1H), 1.56–1.43 (m, 1H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 186.7, 165.7, 133.9, 131.6, 130.9, 129.7, 129.0, 120.2, 79.9, 67.2, 52.5, 33.0, 23.7, 19.5 ppm. IR: ν_max (neat) 3091, 2937, 2808, 1735 cm^–1. HRMS (APCI) m/z: calcd for C₁₆H₁₈⁷⁹BrO₅S [M + H]⁺ 401.0053, found 401.0054.

Allyl-2-(4-fluorobenzoyl)-1,1-dioxo-thiane-2-carboxylate (16f)

25 (436 mg, 2.0 mmol) was dissolved in THF (15 mL). NaHMDS (1 M in THF, 2.20 mL, 2.2 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. 4-Fluorobenzoyl chloride (0.260 mL, 2.2 mmol) was added dropwise, and the mixture was heated at 80 °C for 15 h. The mixture was allowed to cool to room temperature and quenched with aq. HCl (1 N, 25 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (150 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 4:1] gave 16f (564 mg, 83%) as a colorless solid. R_f = 0.61 [petrol:EtOAc 1:1]. m.p.: 88–90 °C. ¹H NMR (400 MHz, CDCl₃) δ 7.96 (dd, J = 9.0, 5.3 Hz, 2H), 7.04 (t, J = 8.7 Hz, 2H), 5.56 (ddt, J = 17.4, 10.4, 6.0 Hz, 1H), 5.16–5.06 (m, 2H), 4.56 (dq, J = 6.4, 1.5 Hz, 2H), 3.60 (dt, J = 14.3, 7.5 Hz, 1H), 3.35 (dt, J = 14.2, 5.4 Hz, 1H), 2.80 (ddd, J = 14.2, 11.0, 3.1 Hz, 1H), 2.51 (ddd, J = 15.1, 7.2, 3.0 Hz, 1H), 2.08–1.99 (m, 2H), 1.73–1.61 (m, 1H), 1.56–1.41 (m, 1H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 185.9, 165.7, 165.7 (d, J = 256.9 Hz), 132.3 (d, J = 9.6 Hz), 131.4 (d, J = 3.0 Hz), 129.7, 120.0, 115.4 (d, J = 22.0 Hz), 79.8, 67.1, 52.4, 33.0, 23.6, 19.4 ppm. ¹⁹F{¹H} NMR (376 MHz, CDCl₃): δ −104.7 ppm. IR: ν_max (neat) 2939, 2868, 1735, 1632 cm^–1. HRMS (APCI) m/z: calcd for C₁₆H₁₈FO₅S [M + H]⁺ 341.0853, found 341.0836.

Allyl-2-(4-methylbenzoyl)-1,1-dioxo-thiane-2-carboxylate (16g)

25 (436 mg, 2.0 mmol) was dissolved in THF (15 mL). NaHMDS (1 M in THF, 2.20 mL, 2.2 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. p-Toluoyl chloride (0.291 mL, 2.2 mmol) was added dropwise, and the mixture was heated at 80 °C for 15 h. The mixture was allowed to cool to room temperature and quenched with aq. HCl (1 N, 25 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (150 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 4:1] gave 16g (580 mg, 86%) as a colorless solid. R_f = 0.67 [petrol:EtOAc 1:1]. m.p.: 112–114 °C. ¹H NMR (400 MHz, CDCl₃) δ 7.78 (d, J = 8.4 Hz, 2H), 7.15 (d, J = 8.1 Hz, 2H), 5.56 (ddt, J = 17.1, 10.4, 5.9 Hz, 1H), 5.12 (dq, J = 17.2, 1.4 Hz, 1H), 5.05 (dq, J = 10.4, 1.1 Hz, 1H), 4.56 (dq, J = 5.8, 1.0 Hz, 2H), 3.55–3.36 (m, 2H), 2.77 (ddd, J = 15.0, 9.7, 3.2 Hz, 1H), 2.56 (ddd, J = 15.0, 7.8, 2.8 Hz, 1H), 2.30 (s, 3H), 2.01 (quint, J = 5.9 Hz, 2H), 1.66–1.44 (m, 2H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 187.2, 165.5, 144.6, 132.2, 129.8, 129.2, 128.9, 119.5, 79.9, 66.9, 52.4, 32.9, 23.6, 21.3, 19.3 ppm. IR: ν_max (neat) 2939, 2868, 1735, 1677 cm^–1. HRMS (APCI) m/z: calcd for C₁₇H₂₁O₅S [M + H]⁺ 337.1104, found 337.1091.

Allyl-2-(4-methoxybenzoyl)-1,1-dioxo-thiane-2-carboxylate (16h)

25 (436 mg, 2.0 mmol) was dissolved in THF (15 mL). NaHMDS (1 M in THF, 2.20 mL, 2.2 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. 4-Methoxybenzoyl chloride (0.298 mL, 2.2 mmol) was added dropwise, and the mixture was heated at 80 °C for 15 h. The mixture was allowed to cool to room temperature and quenched with aq. HCl (1 N, 25 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (150 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 3:1] gave an inseparable mixture of starting material 25 and 16h in a 1:8.1 ratio (673 mg, corresponding to 625 mg of pure 16h, 89%) as a colorless oil. R_f = 0.59 [petrol:EtOAc 1:1]. ¹H NMR (400 MHz, CDCl₃, resonances due to 16h quoted) δ 7.87 (d, J = 9.0 Hz, 2H), 6.82 (d, J = 9.1 Hz, 2H), 5.58 (ddt, J = 17.1, 10.4, 5.9 Hz, 1H), 5.12 (dq, J = 17.2, 1.4 Hz, 1H), 5.06 (dq, J = 10.4, 1.1 Hz, 1H), 4.56 (dq, J = 5.8, 1.5 Hz, 2H), 3.75 (s, 3H), 3.51 (dt, J = 13.5, 6.6 Hz, 1H), 3.43–3.32 (m, 1H), 2.76 (ddd, J = 14.8, 10.1, 3.0 Hz, 1H), 2.52 (ddd, J = 14.9, 7.9, 2.7 Hz, 1H), 2.04–1.96 (m, 2H), 1.67–1.55 (m, J = 5.4, 4.7 Hz, 1H), 1.55–1.42 (m, 1H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃, resonances due to 16h quoted): δ 185.7, 165.8, 163.8, 131.8, 129.9, 127.5, 119.5, 113.4, 79.8, 66.9, 55.2, 52.4, 32.9, 23.6, 19.3 ppm. IR: ν_max (neat) 2939, 1735, 1671 cm^–1. HRMS (ESI) m/z: calcd for C₁₇H₂₀NaO₆S [M + Na]⁺ 375.0873, found 375.0870.

Allyl-2-(furan-2-carbonyl)-1,1-dioxo-thiane-2-carboxylate (16i)

25 (436 mg, 2.0 mmol) was dissolved in THF (15 mL). NaHMDS (1 M in THF, 2.20 mL, 2.2 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. 2-Furoyl chloride (0.217 mL, 2.2 mmol) was added dropwise, and the mixture was heated at 80 °C for 15 h. The mixture was allowed to cool to room temperature and quenched with aq. HCl (1 N, 25 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (150 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 3:1] gave an inseparable mixture of starting material 25 and 16i in a 1:6.8 ratio (497 mg, corresponding to 420 mg of pure 16i, 72%) as a yellow oil. R_f = 0.40 [petrol:EtOAc 1:1]. ¹H NMR (400 MHz, CDCl₃, resonances due to 16i quoted) δ 7.49 (dd, J = 1.6, 0.5 Hz, 1H), 7.23 (dd, J = 3.7, 0.8 Hz, 1H), 6.45 (dd, J = 3.7, 1.7 Hz, 1H), 5.58 (ddt, J = 17.2, 10.4, 5.8 Hz, 1H), 5.09 (dq, J = 17.2, 1.5 Hz, 1H), 5.01 (dq, J = 10.5, 1.2 Hz, 1H), 4.55 (dq, J = 5.9, 1.5 Hz, 2H), 3.46–3.26 (m, 2H), 2.59 (ddd, J = 15.2, 7.4, 4.1 Hz, 1H), 2.49 (ddd, J = 15.1, 8.7, 4.0 Hz, 1H), 1.93 (quint, J = 6.1 Hz, 2H), 1.55–1.38 (m, 2H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃, resonances due to 16i quoted): δ 176.3, 163.7, 149.9, 147.3, 130.1, 120.5, 119.0, 112.6, 79.0, 66.7, 52.2, 31.4, 23.4, 19.0 ppm. IR: ν_max (neat) 3144, 2950, 1748, 1649, 1317, 1125 cm^–1. HRMS (APCI) m/z: calcd for C₁₄H₁₇O₆S [M + H]⁺ 313.0740, found 313.0731.

Allyl-2-(2-methylpropanoyl)-1,1-dioxo-thiane-2-carboxylate (16j)

25 (300 mg, 1.37 mmol) was dissolved in THF (20 mL). NaHMDS (1 M in THF, 1.51 mL, 1.51 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. Isobutyryl chloride (0.150 mL, 1.51 mmol) was added dropwise, and the mixture was heated at 80 °C for 15 h. The mixture was allowed to cool to room temperature and quenched with aq. HCl (1 N, 25 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (150 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 9:1–4:1] gave 16j (191 mg, 48%) as a yellow oil. R_f = 0.32 [petrol:EtOAc 4:1]. ¹H NMR (400 MHz, CDCl₃) δ 5.89 (ddt, J = 17.2, 10.3, 6.1 Hz, 1H), 5.38 (dq, J = 17.2, 1.4 Hz, 1H), 5.30 (dq, J = 10.4, 1.1 Hz, 1H), 4.81–4.65 (m, 2H), 3.60 (ddd, J = 15.0, 9.5, 6.3 Hz, 1H), 3.20 (dt, J = 14.0, 5.0 Hz, 1H), 3.05 (hept, J = 6.6 Hz, 1H), 2.48 (ddd, J = 15.0, 11.5, 3.4 Hz, 1H), 2.41–2.32 (m, 1H), 2.08–1.99 (m, 2H), 1.76–1.65 (m, 1H), 1.58–1.46 (m, 1H), 1.16 (d, J = 6.6 Hz, 3H), 1.11 (d, J = 6.7 Hz, 3H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 202.4, 165.1, 130.2, 120.7, 81.4, 67.4, 52.4, 40.6, 31.3, 24.0, 20.7, 19.9, 19.9 ppm. IR: ν_max (neat) 2976, 2939, 2876, 1744, 1716 cm^–1. HRMS (APCI) m/z: calcd for C₁₃H₂₁O₅S [M + H]⁺ 289.1104, found 289.1097.

Allyl-2-(cyclohexanecarbonyl)-1,1-dioxo-thiane-2-carboxylate (16k)

25 (436 mg, 2.0 mmol) was dissolved in THF (15 mL). NaHMDS (1 M in THF, 2.20 mL, 2.2 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. Cyclohexanecarbonyl chloride (0.294 mL, 2.2 mmol) was added dropwise, and the mixture was heated at 80 °C for 15 h. The mixture was allowed to cool to room temperature and quenched with aq. HCl (1 N, 25 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (150 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 4:1] gave 16k (403 mg, 61%) as a colorless solid. R_f = 0.71 [petrol:EtOAc 1:1]. m.p.: 78–79 °C. ¹H NMR (400 MHz, CDCl₃) δ 5.81 (ddt, J = 16.5, 10.4, 6.0 Hz, 1H), 5.29 (dq, J = 17.2, 1.2 Hz, 1H), 5.21 (dq, J = 10.4, 1.0 Hz, 1H), 4.64 (dtd, J = 5.7, 2.4, 1.1 Hz, 2H), 3.48 (ddd, J = 14.4, 9.9, 5.0 Hz, 1H), 3.10 (dt, J = 14.0, 4.7 Hz, 1H), 2.65 (tt, J = 11.4, 3.1 Hz, 1H), 2.36 (ddd, J = 14.8, 11.3, 3.3 Hz, 1H), 2.25 (ddt, J = 15.2, 5.3, 2.6 Hz, 1H), 2.00–1.88 (m, 3H), 1.68–1.50 (m, 5H), 1.48–1.27 (m, 2H), 1.25–1.06 (m, 4H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 200.5, 164.7, 130.0, 120.2, 81.0, 67.0, 52.0, 50.4, 30.9, 30.2, 29.2, 25.2, 25.0, 24.9, 23.6, 19.5 ppm. IR: ν_max (neat) 2926, 2853, 1746, 1716 cm^–1. HRMS (APCI) m/z: calcd for C₁₆H₂₅O₅S [M + H]⁺ 329.1417, found 329.1427.

Allyl-2-(tetrahydropyran-4-carbonyl)-1,1-dioxo-thiane-2-carboxylate (16l)

25 (436 mg, 2.0 mmol) was dissolved in THF (15 mL). NaHMDS (1 M in THF, 2.20 mL, 2.2 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. Tetrahydro-2H-pyran-4-carbonyl chloride (327 mg, 2.2 mmol) was added, and the mixture was heated at 80 °C for 15 h. The mixture was allowed to cool to room temperature and quenched with aq. HCl (1 N, 25 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (150 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 3:1] gave an inseparable mixture of starting material 25 and 16l in a 1:4.1 ratio (504 mg, corresponding to 434 mg of pure 16l, 66%) as a colorless oil. R_f = 0.62 [petrol:EtOAc 1:1]. ¹H NMR (400 MHz, CDCl₃, resonances due to 16l quoted) δ 5.80–5.66 (m, 1H), 5.21 (dq, J = 17.2, 1.4 Hz, 1H), 5.14 (dd, J = 10.4, 1.1 Hz, 1H), 4.61–4.53 (m, 2H), 3.73 (ddd, J = 12.0, 4.4, 2.0 Hz, 2H), 3.49 (ddd, J = 14.3, 12.0, 4.2 Hz, 1H), 3.16 (tt, J = 11.8, 2.2 Hz, 2H), 2.99 (dt, J = 14.2, 4.3 Hz, 1H), 2.91 (tt, J = 11.5, 3.6 Hz, 1H), 2.28 (ddd, J = 15.4, 12.4, 3.3 Hz, 1H), 2.18–2.08 (m, 1H), 1.96–1.79 (m, 2H), 1.79–1.71 (m, 1H), 1.60 (td, J = 12.3, 4.1 Hz, 2H), 1.51–1.31 (m, 3H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃, resonances due to 16l quoted): δ 198.6, 164.4, 129.9, 120.2, 80.5, 66.8, 66.2, 66.0, 51.8, 47.3, 30.7, 29.5, 28.8, 23.3, 19.2 ppm. IR: ν_max (neat) 2957, 2853, 1746, 1716 cm^–1. HRMS (APCI) m/z: calcd for C₁₅H₂₃O₆S [M + H]⁺ 331.1210, found 331.1207.

Allyl-2-(2,2-dimethylpropanoyl)-1,1-dioxo-thiane-2-carboxylate (16m)

25 (436 mg, 2.0 mmol) was dissolved in THF (15 mL). NaHMDS (1 M in THF, 2.20 mL, 2.2 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. Pivaloyl chloride (0.271 mL, 2.2 mmol) was added dropwise, and the mixture was heated at 80 °C for 15 h. The mixture was allowed to cool to room temperature and quenched with aq. HCl (1 N, 25 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (150 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 4:1] gave 16m (138 mg, 23%) as a colorless oil. R_f = 0.69 [petrol:EtOAc 1:1]. ¹H NMR (400 MHz, CDCl₃) δ 5.88 (ddt, J = 17.3, 10.4, 5.9 Hz, 1H), 5.37 (dq, J = 17.2, 1.4 Hz, 1H), 5.27 (dq, J = 10.4, 1.1 Hz, 1H), 4.70 (ddt, J = 5.8, 2.3, 1.3 Hz, 2H), 3.47–3.32 (m, 2H), 2.56 (ddd, J = 15.3, 8.9, 3.8 Hz, 1H), 2.43 (ddd, J = 15.3, 7.6, 3.8 Hz, 1H), 1.99 (quint, J = 6.6, 6.2 Hz, 2H), 1.62–1.42 (m, 2H), 1.21 (s, 9H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 203.2, 164.6, 130.1, 120.2, 81.3, 67.1, 52.7, 46.9, 32.4, 27.9, 23.8, 19.6 ppm. IR: ν_max (neat) 2939, 1742, 1697 cm^–1. HRMS (APCI) m/z: calcd for C₁₄H₂₃O₅S [M + H]⁺ 303.1261, found 303.1267.

Allyl-2-acetyl-1,1-dioxo-thiane-2-carboxylate (16n)

25 (300 mg, 1.37 mmol) was dissolved in THF (20 mL). NaHMDS (1 M in THF, 1.51 mL, 1.51 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. Acetyl chloride (0.110 mL, 1.51 mmol) was added dropwise, and the mixture was heated at 80 °C for 15 h. The mixture was allowed to cool to room temperature and quenched with aq. HCl (1 N, 25 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (150 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 9:1–4:1] gave 16n (132 mg, 37%) as a yellow oil. R_f = 0.33 [petrol:EtOAc 4:1]. ¹H NMR (300 MHz, CDCl₃) δ 5.90 (ddt, J = 17.2, 10.4, 5.9 Hz, 1H), 5.38 (dq, J = 17.1, 1.4 Hz, 1H), 5.32 (dq, J = 10.4, 1.1 Hz, 1H), 4.74 (dtd, J = 6.0, 1.5, 1.0 Hz, 2H), 3.74–3.57 (m, 1H), 3.17 (dt, J = 13.7, 4.3 Hz, 1H), 2.53–2.31 (m, 5H), 2.14–1.98 (m, 2H), 1.83–1.70 (m, 1H), 1.70–1.51 (m, 1H) ppm. ¹³C{¹H} NMR (75 MHz, CDCl₃): δ 194.1, 165.0, 130.2, 120.5, 80.7, 67.3, 52.1, 31.1, 29.6, 23.9, 19.7 ppm. IR: ν_max (neat) 2939, 2870, 1718 cm^–1. HRMS (APCI) m/z: calcd for C₁₁H₁₇O₅S [M + H]⁺ 261.0791, found 261.0786.

2-Allyl-2′-phenyl-4-tert-butyl-1,1-dioxo-1,4-thiazinane-2,2,4-tricarboxylate (17a)

26 (638 mg, 2.0 mmol) was dissolved in THF (15 mL). NaHMDS (1 M in THF, 2.20 mL, 2.2 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. Phenyl chloroformate (0.276 mL, 2.2 mmol) was added dropwise, and the mixture was stirred for 15 h. The reaction was quenched with aq. HCl (1 N, 25 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (150 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 6:1] gave 17a (741 mg, 84%) as a colorless solid. R_f = 0.53 [petrol:EtOAc 2:1]. m.p.: 103–105 °C. ¹H NMR (400 MHz, DMSO-d₆, 130 °C) δ 7.47 (t, J = 8.2 Hz, 2H), 7.34 (tt, J = 7.4, 1.2 Hz, 1H), 7.17 (dd, J = 8.6, 1.1 Hz, 2H), 5.99 (ddt, J = 17.2, 10.9, 5.5 Hz, 1H), 5.45 (dq, J = 17.3, 1.5 Hz, 1H), 5.32 (dq, J = 10.6, 1.3 Hz, 1H), 4.84 (ddt, J = 7.0, 5.6, 1.4 Hz, 2H), 4.38 (s, 2H), 3.99 (ddd, J = 14.8, 6.8, 4.3 Hz, 1H), 3.90 (ddd, J = 14.7, 7.2, 4.2 Hz, 1H), 3.66–3.52 (m, 2H), 1.43 (s, 9H) ppm. ¹³C{¹H} NMR (100 MHz, DMSO-d₆, 130 °C): δ 161.3, 160.4, 152.5, 149.3, 130.3, 129.0, 126.0, 120.0, 118.3, 80.5, 74.8, 66.7, 50.6, 48.1, 41.8, 27.2 ppm. IR: ν_max (neat) 2978, 1742, 1701 cm^–1. HRMS (ESI) m/z: calcd for C₂₀H₂₅NNaO₈S [M + Na]⁺ 462.1193, found 462.1199.

2-Allyl-2′-benzyl-4-tert-butyl-1,1-dioxo-1,4-thiazinane-2,2,4-tricarboxylate (17b)

26 (638 mg, 2.0 mmol) was dissolved in THF (15 mL). NaHMDS (1 M in THF, 2.20 mL, 2.2 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. Benzyl chloroformate (0.314 mL, 2.2 mmol) was added dropwise, and the mixture was stirred for 15 h. The reaction was quenched with aq. HCl (1 N, 25 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (150 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 6:1] gave 17b (755 mg, 83%) as a colorless oil. R_f = 0.53 [petrol:EtOAc 2:1]. ¹H NMR (400 MHz, DMSO-d₆, 130 °C) δ 7.40–7.35 (m, 5H), 5.83 (ddt, J = 17.2, 10.8, 5.5 Hz, 1H), 5.33 (dq, J = 17.2, 1.6 Hz, 1H), 5.32 (d, J = 12.5 Hz, 1H), 5.26 (d, J = 12.6 Hz, 1H), 5.22 (dq, J = 10.6, 1.3 Hz, 1H), 4.69 (ddt, J = 8.6, 5.5, 1.5 Hz, 2H), 4.31–4.22 (m, 2H), 3.89 (q, J = 5.8 Hz, 2H), 3.52 (ddd, J = 6.2, 4.9, 0.7 Hz, 2H), 1.43 (s, 9H) ppm. ¹³C{¹H} NMR (100 MHz, DMSO-d₆, 130 °C): δ 161.5, 161.4, 152.4, 133.9, 130.2, 127.6, 127.6, 127.1, 118.0, 80.3, 74.6, 67.6, 66.3, 50.4, 48.2, 41.7, 27.2 ppm. IR: ν_max (neat) 2978, 1735, 1701 cm^–1. HRMS (ESI) m/z: calcd for C₂₁H₂₇NNaO₈S [M + Na]⁺ 476.1350, found 476.1364.

2-Allyl-4-tert-butyl-2-benzoyl-1,1-dioxo-1,4-thiazinane-2,4-dicarboxylate (17c)

26 (638 mg, 2.0 mmol) was dissolved in THF (15 mL). NaHMDS (1 M in THF, 2.20 mL, 2.2 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. Benzoyl chloride (0.256 mL, 2.2 mmol) was added dropwise, and the mixture was heated at 80 °C for 15 h. The mixture was allowed to cool to room temperature and quenched with aq. HCl (1 N, 25 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (150 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 6:1] gave 17c (535 mg, 63%) as a colorless solid. R_f = 0.45 [petrol:EtOAc 2:1]. m.p.: 149–150 °C. ¹H NMR (400 MHz, DMSO-d₆, 130 °C) δ 7.85 (dd, J = 8.5, 1.2 Hz, 2H), 7.67 (tt, J = 7.6, 1.6 Hz, 1H), 7.53 (t, J = 7.2 Hz, 2H), 5.69 (ddt, J = 17.2, 10.5, 5.7 Hz, 1H), 5.20 (dq, J = 17.3, 1.5 Hz, 1H), 5.15 (dq, J = 10.5, 1.3 Hz, 1H), 4.67 (ddt, J = 13.2, 5.7, 1.4 Hz, 1H), 4.58 (ddt, J = 13.2, 5.7, 1.4 Hz, 1H), 4.48 (d, J = 4.1 Hz, 2H), 3.92 (ddt, J = 15.5, 10.3, 5.8 Hz, 2H), 3.62 (ddd, J = 6.6, 4.9, 3.8 Hz, 2H), 1.29 (s, 9H) ppm. ¹³C{¹H} NMR (100 MHz, DMSO-d₆, 130 °C): δ 187.4, 163.1, 152.3, 134.9, 133.1, 129.8, 127.9, 127.9, 118.5, 80.3, 78.8, 66.4, 51.2, 49.3, 41.6, 26.9 ppm. IR: ν_max (neat) 2976, 2933, 1735, 1697, 1671 cm^–1. HRMS (ESI) m/z: calcd for C₂₀H₂₅NNaO₇S [M + Na]⁺ 446.1244, found 446.1239.

2-Allyl-4-tert-butyl-2-(2-methylpropanoyl)-1,1-dioxo-1,4-thiazinane-2,4-dicarboxylate (17d)

26 (638 mg, 2.0 mmol) was dissolved in THF (15 mL). NaHMDS (1 M in THF, 2.20 mL, 2.2 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. Isobutyryl chloride (0.234 mL, 2.2 mmol) was added dropwise, and the mixture was heated at 80 °C for 15 h. The mixture was allowed to cool to room temperature and quenched with aq. HCl (1 N, 25 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (150 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 9:1] gave 17d (496 mg, 64%) as a colorless solid. R_f = 0.61 [petrol:EtOAc 2:1]. m.p.: 86–88 °C. ¹H NMR (400 MHz, DMSO-d₆, 130 °C) δ 5.96 (ddt, J = 17.2, 10.5, 5.8 Hz, 1H), 5.43 (dq, J = 17.2, 1.5 Hz, 1H), 5.32 (dq, J = 10.5, 1.2 Hz, 1H), 4.75 (tt, J = 5.7, 1.4 Hz, 2H), 4.41 (dd, J = 15.0, 2.0 Hz, 1H), 4.13 (dtd, J = 11.5, 4.6, 1.8 Hz, 1H), 3.95 (d, J = 15.0 Hz, 1H), 3.63 (d, J = 10.8 Hz, 1H), 3.57 (d, J = 11.0 Hz, 1H), 3.42 (dd, J = 10.6, 5.2 Hz, 1H), 3.07 (hept, J = 6.6 Hz, 1H), 1.43 (s, 9H), 1.15 (d, J = 6.7 Hz, 3H), 1.12 (d, J = 6.6 Hz, 3H) ppm. ¹³C{¹H} NMR (100 MHz, DMSO-d₆, 130 °C): δ 200.7, 162.8, 152.4, 130.1, 118.9, 80.2, 79.1, 66.6, 50.8, 47.8, 41.7, 39.5, 27.2, 19.1, 18.4 ppm. IR: ν_max (neat) 2978, 2946, 1716, 1694 cm^–1. HRMS (ESI) m/z: calcd for C₁₇H₂₇NNaO₇S [M + Na]⁺ 412.1400, found 412.1416.

Synthesis of Allylated Products 18–20

(2R)-Benzyl-2-allyltetrahydrothiophene-2-carboxylate-1,1-dioxide (18a)

A vial was charged with 15a (51 mg, 0.15 mmol), [Pd₂dba₃] (3.5 mg, 3.75 μmol), L4 (8.0 mg, 9.75 μmol), and 1,4-dioxane (1.5 mL). The mixture was stirred at room temperature for 2 h and then concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 4:1] gave 18a (40 mg, 91%) as a yellow oil. R_f = 0.20 [petrol:EtOAc 4:1]. ¹H NMR (400 MHz, CDCl₃) δ 7.44–7.29 (m, 5H), 5.55 (dddd, J = 16.7, 10.1, 7.9, 6.4 Hz, 1H), 5.29 (d, J = 12.3 Hz, 1H), 5.19 (d, J = 12.2 Hz, 1H), 5.16–5.08 (m, 2H), 3.25–3.16 (m, 1H), 3.15–3.03 (m, 2H), 2.81–2.72 (m, 1H), 2.42 (ddt, J = 14.1, 7.9, 1.1 Hz, 1H), 2.31–2.18 (m, 1H), 2.14–2.01 (m, 2H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 167.4, 134.9, 130.9, 128.5, 128.4, 128.4, 120.5, 70.2, 68.3, 51.3, 37.1, 30.8, 18.3 ppm. IR: ν_max (neat) 3066, 3034, 2954, 1733 cm^–1. HRMS (ESI) m/z: calcd for C₁₅H₁₉O₄S [M + H]⁺ 295.0999, found 295.0986. HPLC: 86% ee (Chiralpak AD-H, hexane:i-PrOH = 95:5, flow rate = 1 mL/min, 30.0 °C, λ = 220 nm) t_R = 20.8 min (major), t_R = 22.9 min (minor). [α]: −55.1 (c = 0.12, CHCl₃).

(2R)-Phenyl-2-allyltetrahydrothiophene-2-carboxylate-1,1-dioxide (18b)

A vial was charged with 15b (48.5 mg, 0.15 mmol), [Pd₂dba₃] (3.5 mg, 3.75 μmol), L4 (8.0 mg, 9.75 μmol), and 1,4-dioxane (1.5 mL). The mixture was stirred at room temperature for 2 h and then concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 4:1] gave 18b (39 mg, 90%) as a yellow oil. R_f = 0.20 [petrol:EtOAc 4:1]. ¹H NMR (300 MHz, CDCl₃) δ 7.43–7.35 (m, 2H), 7.25 (tt, J = 7.4, 1.3 Hz, 1H), 7.15 (d, J = 7.4 Hz, 2H), 5.79 (ddt, J = 17.1, 10.0, 7.1 Hz, 1H), 5.37–5.23 (m, 2H), 3.35–3.22 (m, 2H), 3.21–3.09 (m, 1H), 2.94–2.82 (m, 1H), 2.54 (ddt, J = 14.2, 7.5, 1.1 Hz, 1H), 2.38–2.24 (m, 1H), 2.20–2.08 (m, 2H) ppm. ¹³C{¹H} NMR (75 MHz, CDCl₃): δ 166.4, 150.6, 130.9, 129.5, 126.4, 121.4, 120.9, 70.3, 51.8, 37.4, 31.2, 18.6 ppm. IR: ν_max (neat) 3079, 2952, 1750 cm^–1. HRMS (APCI) m/z: calcd for C₁₄H₁₇O₄S [M + H]⁺ 281.0842, found 281.0832. HPLC: 94% ee (Chiralcel OD-H, hexane:i-PrOH = 90:10, flow rate = 1 mL/min, 30.0 °C, λ = 220 nm) t_R = 14.4 min (major), t_R = 17.4 min (minor). [α]: −68.5 (c = 0.07, CHCl₃).

(2R)-4-Methoxyphenyl-2-allyltetrahydrothiophene-2-carboxylate-1,1-dioxide (18c)

A vial was charged with a 1:2.3 mixture of 24:15c (67 mg, corresponding to 53.5 mg of pure 15c, 0.15 mmol), [Pd₂dba₃] (3.5 mg, 3.75 μmol), L4 (8.0 mg, 9.75 μmol), and 1,4-dioxane (1.5 mL). The mixture was stirred at room temperature for 2 h and then concentrated under reduced pressure. Purification by flash column chromatography [petrol:EtOAc 2:1] gave 18c (27.5 mg, 59%) as a colorless solid. R_f = 0.28 [petrol:EtOAc 2:1]. m.p.: 88–89 °C. ¹H NMR (400 MHz, CDCl₃) δ 7.06 (d, J = 9.1 Hz, 2H), 6.88 (d, J = 9.1 Hz, 2H), 5.77 (ddt, J = 17.1, 9.9, 7.2 Hz, 1H), 5.32 (d, J = 17.0 Hz, 1H), 5.27 (d, J = 10.3 Hz, 1H), 3.79 (s, 3H), 3.27 (dt, J = 13.4, 6.7 Hz, 2H), 3.14 (dt, J = 12.7, 7.5 Hz, 1H), 2.92–2.83 (m, 1H), 2.53 (dd, J = 14.3, 7.4 Hz, 1H), 2.36–2.25 (m, 1H), 2.13 (ddd, J = 13.8, 11.2, 6.3 Hz, 2H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 166.7, 157.6, 144.1, 131.0, 122.1, 120.8, 114.5, 70.2, 55.6, 51.7, 37.3, 31.2, 18.5 ppm. IR: ν_max (neat) 2945, 1752 cm^–1. HRMS (APCI) m/z: calcd for C₁₅H₁₈NaO₅S [M + Na]⁺ 333.0767, found 333.0755. HPLC: 93% ee (Chiralpak AD-H, hexane:i-PrOH = 90:10, flow rate = 1 mL/min, 30.0 °C, λ = 220 nm) t_R = 22.1 min (major), t_R = 26.2 min (minor). [α]: −46.7 (c = 0.23, CHCl₃).

(2R)-p-Tolyl-2-allyltetrahydrothiophene-2-carboxylate-1,1-dioxide (18d)

A vial was charged with 15d (51 mg, 0.15 mmol), [Pd₂dba₃] (3.5 mg, 3.75 μmol), L4 (8.0 mg, 9.75 μmol), and 1,4-dioxane (1.5 mL). The mixture was stirred at room temperature for 2 h and then concentrated under reduced pressure. Purification by flash column chromatography [petrol:EtOAc 4:1] gave 18d (38.5 mg, 88%) as colorless crystals. R_f = 0.37 [petrol:EtOAc 2:1]. m.p.: 106–108 °C. ¹H NMR (400 MHz, CDCl₃) δ 7.17 (d, J = 8.7 Hz, 2H), 7.02 (d, J = 8.5 Hz, 2H), 5.77 (ddt, J = 17.1, 10.0, 7.2 Hz, 1H), 5.33 (dd, J = 17.0, 1.5 Hz, 1H), 5.27 (dd, J = 10.2, 1.6 Hz, 1H), 3.33–3.23 (m, 2H), 3.18–3.10 (m, 1H), 2.92–2.82 (m, 1H), 2.53 (dd, J = 14.1, 7.5 Hz, 1H), 2.34 (s, 3H), 2.34–2.25 (m, 1H), 2.20–2.08 (m, 2H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 166.5, 148.4, 136.0, 131.0, 130.0, 121.0, 120.8, 70.2, 51.7, 37.3, 31.2, 20.9, 18.5 ppm. IR: ν_max (neat) 2945, 1746 cm^–1. HRMS (APCI) m/z: calcd for C₁₅H₁₉O₄S [M + H]⁺ 295.0999, found 295.0989. HPLC: 84% ee (Chiralpak AD-H, hexane:i-PrOH = 90:10, flow rate = 1 mL/min, 30.0 °C, λ = 220 nm) t_R = 13.4 min (major), t_R = 15.5 min (minor). [α]: −56.2 (c = 0.27, CHCl₃).

(2R)-9H-Fluoren-9-yl-2-allyltetrahydrothiophene-2-carboxylate-1,1-dioxide (18e)

A vial was charged with 15e (64 mg, 0.15 mmol), [Pd₂dba₃] (6.9 mg, 7.5 μmol), L4 (15.9 mg, 19.5 μmol), and 1,4-dioxane (1.5 mL). The mixture was stirred at room temperature for 3 h and then concentrated under reduced pressure. Purification by flash column chromatography [petrol:EtOAc 4:1] gave 18e (42 mg, 76%) as a clear oil. R_f = 0.30 [petrol:EtOAc 2:1]. ¹H NMR (400 MHz, CDCl₃) δ 7.76 (d, J = 7.5 Hz, 2H), 7.68 (d, J = 7.5 Hz, 1H), 7.63 (d, J = 7.4 Hz, 1H), 7.41 (t, J = 7.5 Hz, 2H), 7.34 (t, J = 7.3 Hz, 2H), 5.44 (dddd, J = 16.1, 9.8, 8.1, 6.0 Hz, 1H), 5.16–5.04 (m, 2H), 4.79 (dd, J = 10.8, 5.5 Hz, 1H), 4.45 (dd, J = 10.7, 6.6 Hz, 1H), 4.28 (t, J = 6.1 Hz, 1H), 3.13–2.96 (m, 3H), 2.59–2.49 (m, 1H), 2.40 (dd, J = 14.0, 8.2 Hz, 1H), 2.11–1.92 (m, 3H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 167.2, 143.7, 143.2, 141.4, 141.2, 131.0, 127.9, 127.8, 127.2, 125.1, 124.9, 120.3, 119.9, 119.9, 70.1, 67.9, 51.0, 46.8, 36.8, 30.7, 18.1 ppm. IR: ν_max (neat) 2945, 1733 cm^–1. HRMS (ESI) m/z: calcd for C₂₂H₂₂NaO₄S [M + Na]⁺ 405.1131, found 405.1128. HPLC: 80% ee (Chiralpak AD-H, hexane:i-PrOH = 90:10, flow rate = 1 mL/min, 30.0 °C, λ = 245 nm) t_R = 20.1 min (major), t_R = 28.6 min (minor). [α]: +4.7 (c = 0.69, CHCl₃).

(2R)-Allyl-2-allyl-1,1-dioxo-thiolane-2-carboxylate (18f)

A vial was charged with 15f (43 mg, 0.15 mmol), [Pd₂dba₃] (6.9 mg, 7.5 μmol), L4 (15.9 mg, 19.5 μmol), and 1,4-dioxane (1.5 mL). The mixture was stirred at room temperature for 15 h and then concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 5:1] gave 18f (19.5 mg, 53%) as a colorless oil. R_f = 0.36 [petrol:EtOAc 2:1]. ¹H NMR (400 MHz, CDCl₃) δ 5.94 (ddt, J = 17.2, 10.4, 5.9 Hz, 1H), 5.68–5.55 (m, 1H), 5.39 (dq, J = 17.2, 1.5 Hz, 1H), 5.28 (dq, J = 10.4, 1.2 Hz, 1H), 5.25–5.14 (m, 2H), 4.72 (tt, J = 6.0, 1.4 Hz, 2H), 3.27–3.16 (m, 1H), 3.18–3.03 (m, 2H), 2.82–2.71 (m, 1H), 2.43 (ddt, J = 14.1, 7.9, 0.9 Hz, 1H), 2.34–2.18 (m, 1H), 2.16–2.00 (m, 2H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 167.0, 131.2, 131.1, 120.6, 119.3, 70.2, 67.1, 51.3, 37.1, 30.8, 18.3 ppm. IR: ν_max (neat) 3082, 2952, 1733 cm^–1. HRMS (APCI) m/z: calcd for C₁₁H₁₇O₄S [M + H]⁺ 245.0842, found 245.0846. HPLC: 85% ee (Chiralpak AD-H, hexane:i-PrOH = 95:5, flow rate = 1 mL/min, 30.0 °C, λ = 235 nm) t_R = 11.0 min (minor), t_R = 11.6 min (major). [α]: −42.3 (c = 0.13, CHCl₃).

(2R)-Isobutyl-2-allyl-1,1-dioxo-thiolane-2-carboxylate (18g)

A vial was charged with 15g (47 mg, 0.15 mmol), [Pd₂dba₃] (6.9 mg, 7.5 μmol), L4 (15.9 mg, 19.5 μmol), and 1,4-dioxane (1.5 mL). The mixture was stirred at room temperature for 15 h and then concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 4:1] gave 18g (24 mg, 62%) as a colorless oil. R_f = 0.66 [petrol:EtOAc 1:1]. ¹H NMR (400 MHz, CDCl₃) δ 5.62 (dddd, J = 16.6, 10.1, 8.0, 6.3 Hz, 1H), 5.24–5.15 (m, 2H), 4.04 (dd, J = 10.5, 6.4 Hz, 1H), 3.96 (dd, J = 10.5, 6.7 Hz, 1H), 3.25–3.16 (m, 1H), 3.16–3.04 (m, 2H), 2.80–2.72 (m, 1H), 2.43 (dd, J = 14.1, 8.0 Hz, 1H), 2.31–2.19 (m, 1H), 2.13–1.96 (m, 3H), 0.98 (d, J = 1.3 Hz, 3H), 0.96 (d, J = 1.3 Hz, 3H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 167.3, 131.2, 120.4, 72.7, 70.3, 51.3, 37.1, 30.8, 27.6, 19.1, 19.0, 18.3 ppm. IR: ν_max (neat) 2961, 2875, 1733 cm^–1. HRMS (APCI) m/z: calcd for C₁₂H₂₁O₄S [M + H]⁺ 261.1155, found 261.1154. HPLC: 95% ee (Chiralpak AD-H, hexane:i-PrOH = 95:5, flow rate = 1 mL/min, 30.0 °C, λ = 210 nm) t_R = 8.7 min (major), t_R = 18.7 min (minor). [α]: −16.8 (c = 0.21, CHCl₃).

(2R)-Methyl-2-allyl-tetrahydrothiophene-2-carboxylate-1,1-dioxide (18h)

A vial was charged with 15h (77 mg, 0.29 mmol), [Pd₂dba₃] (6.7 mg, 7.3 μmol), L4 (15.3 mg, 18.9 μmol), and 1,4-dioxane (2.9 mL). The mixture was stirred at room temperature for 2 h and then concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 4:1] gave 18h (58 mg, 92%) as a colorless oil. R_f = 0.32 [petrol:EtOAc 4:1]. ¹H NMR (400 MHz, CDCl₃) δ 5.61 (dddd, J = 17.0, 10.1, 7.9, 6.4 Hz, 1H), 5.24–5.15 (m, 2H), 3.84 (s, 3H), 3.25–3.17 (m, 1H), 3.14–3.04 (m, 2H), 2.81–2.72 (m, 1H), 2.42 (ddt, J = 14.2, 7.9, 1.1 Hz, 1H), 2.32–2.20 (m, 1H), 2.15–2.01 (m, 2H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 167.8, 131.1, 120.5, 70.3, 53.4, 51.3, 37.1, 30.8, 18.4 ppm. IR: ν_max (neat) 3081, 3006, 2954, 1735 cm^–1. HRMS (APCI) m/z: calcd for C₉H₁₅O₄S [M + H]⁺ 219.0686, found 219.0680. HPLC: 69% ee (Chiralcel OD-H, hexane:i-PrOH = 95:5, flow rate = 1 mL/min, 30.0 °C, λ = 220 nm) t_R = 17.3 min (minor), t_R = 19.0 min (major). [α]: −56.7 (c = 0.30, CHCl₃).

(2R)-Phenyl-2-(2-methylallyl)tetrahydrothiophene-2-carboxylate-1,1-dioxide (18i)

A vial was charged with 15i (30 mg, 0.089 mmol), [Pd₂dba₃] (2.1 mg, 2.5 μmol), L4 (4.7 mg, 5.8 μmol), and 1,4-dioxane (0.9 mL). The mixture was stirred at room temperature for 2 h and then concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 19:1–4:1] gave 18i (16 mg, 62%) as a colorless oil. R_f = 0.21 [petrol:EtOAc 4:1]. ¹H NMR (300 MHz, CDCl₃) δ 7.39 (t, J = 7.7 Hz, 2H), 7.25 (tt, J = 7.4, 1.2 Hz, 1H), 7.16 (d, J = 7.4 Hz, 2H), 4.99 (t, J = 1.7 Hz, 1H), 4.86 (t, J = 1.2 Hz, 1H), 3.34 (d, J = 15.4 Hz, 1H), 3.30–3.21 (m, 1H), 3.20–3.07 (m, 1H), 3.01–2.88 (m, 1H), 2.56 (d, J = 15.4 Hz, 1H), 2.42–2.02 (m, 3H), 1.83 (s, 3H) ppm. ¹³C{¹H} NMR (75 MHz, CDCl₃): δ 167.0, 150.7, 139.6, 129.5, 126.4, 121.3, 115.3, 70.0, 51.4, 40.4, 31.1, 23.3, 18.6 ppm. IR: ν_max (neat) 3075, 2948, 1752 cm^–1. HRMS (APCI) m/z: calcd for C₁₅H₁₉O₄S [M + H]⁺ 295.0999, found 295.0999. HPLC: 82% ee (Chiralcel OD-H, hexane:i-PrOH = 95:5, flow rate = 1 mL/min, 30.0 °C, λ = 220 nm) t_R = 18.9 min (major), t_R = 20.9 min (minor). [α]: −217 (c = 0.05, CHCl₃).

(2R)-(p-Tolyl)-2-(2-methylallyl)tetrahydrothiophene-2-carboxylate-1,1-dioxide (18j)

A vial was charged with 15j (30 mg, 0.085 mmol), [Pd₂dba₃] (2.1 mg, 2.1 μmol), L4 (4.5 mg, 5.5 μmol), and 1,4-dioxane (0.9 mL). The mixture was stirred at room temperature for 2 h and then concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 19:1–4:1] gave 18j (16 mg, 60%) as a colorless oil. R_f = 0.25 [petrol:EtOAc 4:1]. ¹H NMR (300 MHz, CDCl₃) δ 7.17 (d, J = 8.8 Hz, 2H), 7.03 (d, J = 8.6 Hz, 2H), 4.98 (dq, J = 2.6, 1.4 Hz, 1H), 4.85 (quint, J = 1.2 Hz, 1H), 3.32 (d, J = 14.5 Hz, 1H), 3.29–3.20 (m, 1H), 3.19–3.07 (m, 1H), 2.99–2.86 (m, 1H), 2.55 (dd, J = 15.3, 1.0 Hz, 1H), 2.34 (s, 3H), 2.33–2.24 (m, 1H), 2.24–2.05 (m, 2H), 1.81 (dt, J = 1.5, 0.7 Hz, 3H) ppm. ¹³C{¹H} NMR (75 MHz, CDCl₃): δ 167.1, 148.5, 139.7, 136.0, 130.0, 121.0, 115.3, 70.0, 51.4, 40.3, 31.0, 23.3, 20.9, 18.6 ppm. IR: ν_max (neat) 3075, 3032, 2948, 1750 cm^–1. HRMS (APCI) m/z: calcd for C₁₆H₂₁O₄S [M + H]⁺ 309.1155, found 309.1145. HPLC: 87% ee (Chiralcel OD-H, hexane:i-PrOH = 95:5, flow rate = 1 mL/min, 30.0 °C, λ = 220 nm) t_R = 18.6 min (major), t_R = 21.6 min (minor). [α]: −100 (c = 0.10, CHCl₃).

(2R)-(2-Allyl-1,1-dioxidotetrahydrothiophen-2-yl)(phenyl)methanone (18k)

A vial was charged with 15k (46 mg, 0.15 mmol), [Pd₂dba₃] (6.9 mg, 7.5 μmol), L4 (15.9 mg, 19.5 μmol), and 1,4-dioxane (1.5 mL). The mixture was stirred at room temperature for 2 h and then concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 4:1] gave 18k (31 mg, 78%) as a colorless oil. R_f = 0.27 [petrol:EtOAc 4:1]. ¹H NMR (300 MHz, CDCl₃) δ 8.00 (d, J = 7.0 Hz, 2H), 7.56 (tt, J = 7.3, 1.4 Hz, 1H), 7.47 (t, J = 7.3 Hz, 2H), 5.32 (dddd, J = 16.7, 10.1, 8.0, 6.5 Hz, 1H), 5.00 (ddt, J = 10.1, 1.8, 1.0 Hz, 1H), 4.88 (dq, J = 16.9, 1.5 Hz, 1H), 3.37–3.03 (m, 4H), 2.64 (ddt, J = 14.6, 7.9, 1.1 Hz, 1H), 2.35–2.01 (m, 3H) ppm. ¹³C{¹H} NMR (75 MHz, CDCl₃): δ 193.9, 136.0, 132.9, 130.1, 129.4, 128.4, 120.7, 73.9, 53.7, 39.4, 32.5, 18.7 ppm. IR: ν_max (neat) 3066, 2950, 1675 cm^–1. HRMS (APCI) m/z: calcd for C₁₄H₁₇O₃S [M + H]⁺ 265.0893, found 265.0885. HPLC: 72% ee (Chiralcel OD-H, hexane:i-PrOH = 90:10, flow rate = 1 mL/min, 30.0 °C, λ = 254 nm) t_R = 13.4 min (minor), t_R = 18.0 min (major). [α]: −44.9 (c = 0.35, CHCl₃).

(2R)-(2-Allyl-1,1-dioxidotetrahydrothiophen-2-yl)(p-tolyl)methanone (18l)

A vial was charged with 15l (30 mg, 0.093 mmol), [Pd₂dba₃] (4.6 mg, 5.0 μmol), L4 (9.8 mg, 12.0 μmol), and 1,4-dioxane (0.9 mL). The mixture was stirred at room temperature for 2 h and then concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 4:1] gave 18l (23 mg, 89%) as a colorless solid. R_f = 0.22 [petrol:EtOAc 4:1]. m.p.: 81–82 °C. ¹H NMR (300 MHz, CDCl₃) δ 7.93 (d, J = 8.5 Hz, 2H), 7.26 (d, J = 7.9 Hz, 2H), 5.33 (dddd, J = 16.6, 10.1, 8.1, 6.4 Hz, 1H), 5.01 (ddt, J = 10.1, 1.8, 1.0 Hz, 1H), 4.90 (dq, J = 16.8, 1.4 Hz, 1H), 3.38–3.02 (m, 4H), 2.63 (ddt, J = 14.6, 8.1, 1.1 Hz, 1H), 2.40 (s, 3H), 2.33–2.00 (m, 3H) ppm. ¹³C{¹H} NMR (75 MHz, CDCl₃): δ 193.1, 143.9, 133.3, 130.2, 129.6, 129.1, 120.6, 73.9, 53.8, 39.5, 32.5, 21.6, 18.7 ppm. IR: ν_max (neat) 3066, 2954, 2926, 2854, 1675 cm^–1. HRMS (APCI) m/z: calcd for C₁₅H₁₉O₃S [M + H]⁺ 279.1049, found 279.1041. HPLC: 62% ee (Chiralcel OD-H, hexane:i-PrOH = 95:5, flow rate = 1 mL/min, 30.0 °C, λ = 220 nm) t_R = 21.2 min (minor), t_R = 33.4 min (major). [α]: −68.8 (c = 0.11, CHCl₃).

(2R)-(2-Allyl-1,1-dioxo-thiolan-2-yl)-(2-furyl)methanone (18m)

A vial was charged with a 1:5.2 mixture of 24:15m (51 mg, corresponding to 44.5 mg of pure 15m, 0.15 mmol), [Pd₂dba₃] (6.9 mg, 7.5 μmol), L4 (15.9 mg, 19.5 μmol), and 1,4-dioxane (1.5 mL). The mixture was stirred at room temperature for 2 h and then concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 5:1] gave 18m (32 mg, 84%) as a yellow oil. R_f = 0.33 [petrol:EtOAc 2:1]. ¹H NMR (400 MHz, CDCl₃) δ 7.67 (dd, J = 1.7, 0.7 Hz, 1H), 7.42 (dd, J = 3.7, 0.8 Hz, 1H), 6.57 (dd, J = 3.7, 1.7 Hz, 1H), 5.46 (dddd, J = 17.0, 10.1, 7.7, 6.9 Hz, 1H), 5.07 (dq, J = 10.1, 1.2 Hz, 1H), 5.02 (dq, J = 16.7, 1.4 Hz, 1H), 3.56 (dd, J = 14.5, 6.9 Hz, 1H), 3.26–3.11 (m, 2H), 3.14–3.02 (m, 1H), 2.63 (ddt, J = 14.5, 7.7, 1.2 Hz, 1H), 2.24–2.06 (m, 2H), 2.09–1.97 (m, 1H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 180.9, 151.9, 146.9, 130.5, 120.5, 120.0, 112.5, 73.1, 53.6, 38.6, 31.1, 18.4 ppm. IR: ν_max (neat) 2953, 1662 cm^–1. HRMS (APCI) m/z: calcd for C₁₂H₁₅O₄S [M + H]⁺ 255.0686, found 255.0680. HPLC: 68% ee (Chiralpak AD-H, hexane:i-PrOH = 95:5, flow rate = 1 mL/min, 30.0 °C, λ = 220 nm) t_R = 22.8 min (minor), t_R = 26.8 min (major). [α]: −59.4 (c = 0.24, CHCl₃).

(2R)-(2-Allyl-1,1-dioxo-thiolan-2-yl)cyclohexylmethanone (18n)

A vial was charged with 15n (47 mg, 0.15 mmol), [Pd₂dba₃] (6.9 mg, 7.5 μmol), L4 (15.9 mg, 19.5 μmol), and 1,4-dioxane (1.5 mL). The mixture was stirred at room temperature for 2 h and then concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 5:1] gave 18n (37 mg, 91%) as a colorless solid. R_f = 0.61 [petrol:EtOAc 2:1]. m.p.: 60–62 °C. ¹H NMR (400 MHz, CDCl₃) δ 5.48 (dddd, J = 17.3, 9.8, 8.5, 5.3 Hz, 1H), 5.22–5.15 (m, 2H), 3.17–3.03 (m, 3H), 2.89 (tt, J = 11.3, 3.1 Hz, 1H), 2.78–2.68 (m, 1H), 2.62 (ddt, J = 15.1, 8.5, 1.0 Hz, 1H), 2.17–2.07 (m, 1H), 2.07–1.94 (m, 3H), 1.83–1.72 (m, 3H), 1.72–1.64 (m, 1H), 1.45–1.22 (m, 5H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 206.6, 130.8, 120.6, 74.9, 51.6, 48.5, 36.2, 30.4, 29.1, 28.6, 25.7, 25.6, 25.4, 17.5 ppm. IR: ν_max (neat) 2929, 2853, 1701 cm^–1. HRMS (APCI) m/z: calcd for C₁₄H₂₃O₃S [M + H]⁺ 271.1362, found 271.1373. HPLC: 89% ee (Chiralcel OD-H, hexane:i-PrOH = 95:5, flow rate = 1 mL/min, 30.0 °C, λ = 225 nm) t_R = 9.0 min (minor), t_R = 9.9 min (major). [α]: −90.2 (c = 0.28, CHCl₃).

(2R)-(2-Allyl-1,1-dioxo-thiolan-2-yl)-tetrahydropyran-4-yl-methanone (18o)

A vial was charged with a 1:3.4 mixture of 24:15o (56.5 mg, corresponding to 47.5 mg of pure 15o, 0.15 mmol), [Pd₂dba₃] (6.9 mg, 7.5 μmol), L4 (15.9 mg, 19.5 μmol), and 1,4-dioxane (1.5 mL). The mixture was stirred at room temperature for 18 h and then concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 3:1] gave 18o (41 mg, quant.) as a colorless solid. R_f = 0.41 [petrol:EtOAc 1:1]. m.p.: 54–57 °C. ¹H NMR (400 MHz, CDCl₃) δ 5.52–5.39 (m, 1H), 5.22 (dt, J = 1.6, 1.0 Hz, 1H), 5.18 (dq, J = 6.6, 1.4 Hz, 1H), 4.03–3.94 (m, 2H), 3.49–3.39 (m, 2H), 3.20–3.03 (m, 4H), 2.76 (dt, J = 13.8, 6.9 Hz, 1H), 2.66 (ddt, J = 15.3, 8.2, 1.0 Hz, 1H), 2.16–1.91 (m, 3H), 1.89–1.69 (m, 3H), 1.64 (ddd, J = 13.3, 3.8, 2.0 Hz, 1H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 204.9, 130.4, 120.9, 75.0, 67.1, 66.8, 51.9, 45.6, 36.3, 30.2, 28.7, 28.7, 17.6 ppm. IR: ν_max (neat) 2957, 2931, 1709 cm^–1. HRMS (APCI) m/z: calcd for C₁₃H₂₁O₄S [M + H]⁺ 273.1155, found 273.1144. HPLC: 91% ee (Chiralpak AD-H, hexane:i-PrOH = 95:5, flow rate = 1 mL/min, 30.0 °C, λ = 200 nm) t_R = 19.7 min (minor), t_R = 20.8 min (major). [α]: −77.0 (c = 0.34, CHCl₃).

(2R)-(2-Allyl-1,1-dioxo-thiolan-2-yl)cyclopropylmethanone (18p)

A vial was charged with 15p (41 mg, 0.15 mmol), [Pd₂dba₃] (6.9 mg, 7.5 μmol), L4 (15.9 mg, 19.5 μmol), and 1,4-dioxane (1.5 mL). The mixture was stirred at room temperature for 2 h and then concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 5:1] gave 18p (34 mg, 99%) as a colorless oil. R_f = 0.66 [petrol:EtOAc 2:1]. ¹H NMR (400 MHz, CDCl₃) δ 5.53 (dddd, J = 16.7, 10.0, 7.8, 6.5 Hz, 1H), 5.25–5.15 (m, 2H), 3.24 (ddd, J = 14.7, 6.6, 1.5 Hz, 1H), 3.19–3.06 (m, 2H), 2.79 (dt, J = 13.9, 7.0 Hz, 1H), 2.62 (ddt, J = 14.7, 7.9, 1.0 Hz, 1H), 2.32 (tt, J = 7.7, 4.5 Hz, 1H), 2.19–1.98 (m, 2H), 1.92 (dt, J = 13.9, 7.0 Hz, 1H), 1.31–1.23 (m, 1H), 1.09–0.97 (m, 3H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 202.7, 130.5, 120.6, 74.5, 51.6, 37.3, 28.9, 19.8, 17.7, 13.9, 12.3 ppm. IR: ν_max (neat) 2952, 1697 cm^–1. HRMS (APCI) m/z: calcd for C₁₁H₁₇O₃S [M + H]⁺ 229.0893, found 229.0890. HPLC: 87% ee (Chiralpak AD-H, hexane:i-PrOH = 95:5, flow rate = 1 mL/min, 30.0 °C, λ = 215 nm) t_R = 12.0 min (minor), t_R = 14.0 min (major). [α]: −51.0 (c = 0.27, CHCl₃).

(2R)-2-(2-Methylpropanoyl)-2-(prop-2-en-1-yl)thiolane-1,1-dione (18q)

A vial was charged with 15q (50 mg, 0.18 mmol), [Pd₂dba₃] (8.2 mg, 9.1 μmol), L4 (19.0 mg, 23.0 μmol), and 1,4-dioxane (1.8 mL). The mixture was stirred at room temperature for 2 h and then concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 4:1] gave 18q (40 mg, 97%) as a yellow oil. R_f = 0.29 [petrol:EtOAc 4:1]. ¹H NMR (400 MHz, CDCl₃) δ 5.46 (dddd, J = 17.2, 9.9, 8.4, 5.6 Hz, 1H), 5.21–5.17 (m, 1H), 5.17–5.12 (m, 1H), 3.19–3.02 (m, 4H), 2.75–2.67 (m, 1H), 2.59 (ddt, J = 15.0, 8.4, 1.1 Hz, 1H), 2.16–1.94 (m, 3H), 1.13 (d, J = 6.6 Hz, 3H), 1.10 (d, J = 6.6 Hz, 3H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 207.8, 130.6, 120.6, 74.8, 51.5, 38.0, 36.2, 28.5, 20.3, 19.6, 17.5 ppm. IR: ν_max (neat) 3083, 2976, 2939, 2876, 1709 cm^–1. HRMS (APCI) m/z: calcd for C₁₁H₁₉O₃S [M + H]⁺ 231.1049, found 231.1042. HPLC: 88% ee (Chiralcel OD-H, hexane:i-PrOH = 95:5, flow rate = 1 mL/min, 30.0 °C, λ = 210 nm) t_R = 10.5 min (minor), t_R = 12.6 min (major). [α]: −173 (c = 0.18, CHCl₃).

(2R)-1-(2-Allyl-1,1-dioxo-thiolan-2-yl)-2,2-dimethylpropan-1-one (18r)

A vial was charged with 15r (43 mg, 0.15 mmol), [Pd₂dba₃] (6.9 mg, 7.5 μmol), L4 (15.9 mg, 19.5 μmol), and 1,4-dioxane (1.5 mL). The mixture was stirred at room temperature for 18 h and then concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 5:1] gave 18r (18 mg, 49%) as a colorless oil. R_f = 0.52 [petrol:EtOAc 2:1]. ¹H NMR (400 MHz, CDCl₃) δ 5.51 (dddd, J = 17.3, 9.8, 8.0, 6.1 Hz, 1H), 5.19 (ddq, J = 14.7, 3.1, 1.6 Hz, 2H), 3.28 (ddq, J = 15.1, 6.1, 1.3 Hz, 1H), 3.19–3.05 (m, 2H), 2.96–2.86 (m, 1H), 2.60 (ddt, J = 15.1, 8.0, 1.1 Hz, 1H), 2.16–1.98 (m, 3H), 1.31 (s, 9H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 207.8, 131.2, 120.6, 76.0, 52.7, 46.3, 37.8, 31.7, 28.3, 18.0 ppm. IR: ν_max (neat) 2972, 1686 cm^–1. HRMS (APCI) m/z: calcd for C₁₂H₂₁O₃S [M + H]⁺ 245.1206, found 245.1207. HPLC: 90% ee (Chiralcel OD-H, hexane:i-PrOH = 95:5, flow rate = 1 mL/min, 30.0 °C, λ = 220 nm) t_R = 11.4 min (minor), t_R = 12.0 min (major). [α]: −35.7 (c = 0.14, CHCl₃).

(2R)-1-(2-Allyl-1,1-dioxo-thiolan-2-yl)-3-methyl-butan-1-one (18s)

A vial was charged with 15s (43 mg, 0.15 mmol), [Pd₂dba₃] (6.9 mg, 7.5 μmol), L4 (15.9 mg, 19.5 μmol), and 1,4-dioxane (1.5 mL). The mixture was stirred at room temperature for 2 h and then concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 5:1] gave 18s (25 mg, 68%) as a colorless oil. R_f = 0.47 [petrol:EtOAc 2:1]. ¹H NMR (400 MHz, CDCl₃) δ 5.57–5.44 (m, 1H), 5.23–5.16 (m, 2H), 3.17–3.01 (m, 3H), 2.79 (dt, J = 13.7, 7.0 Hz, 1H), 2.73 (dd, J = 18.4, 7.0 Hz, 1H), 2.57 (ddt, J = 15.1, 7.3, 1.2 Hz, 1H), 2.48 (dd, J = 18.4, 6.2 Hz, 1H), 2.26–2.12 (m, 2H), 2.04 (dtd, J = 13.5, 7.0, 1.1 Hz, 1H), 1.93 (dt, J = 13.8, 6.8 Hz, 1H), 0.94 (d, J = 2.2 Hz, 3H), 0.93 (d, J = 2.2 Hz, 3H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 202.1, 130.4, 120.6, 73.8, 51.4, 48.9, 36.7, 29.2, 23.7, 22.7, 22.2, 17.7 ppm. IR: ν_max (neat) 2957, 2871, 1712 cm^–1. HRMS (APCI) m/z: calcd for C₁₂H₂₁O₃S [M + H]⁺ 245.1206, found 245.1207. HPLC: 78% ee (Chiralcel OD-H, hexane:i-PrOH = 95:5, flow rate = 1 mL/min, 30.0 °C, λ = 280 nm) t_R = 8.3 min (minor), t_R = 9.3 min (major). [α]: −61.9 (c = 0.21, CHCl₃).

(2R)-1-(2-Allyl-1,1-dioxo-thiolan-2-yl)butan-1-one (18t)

A vial was charged with 15t (41 mg, 0.15 mmol), [Pd₂dba₃] (6.9 mg, 7.5 μmol), L4 (15.9 mg, 19.5 μmol), and 1,4-dioxane (1.5 mL). The mixture was stirred at room temperature for 2 h and then concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 5:1] gave 18t (33 mg, 96%) as a colorless oil. R_f = 0.55 [petrol:EtOAc 2:1]. ¹H NMR (400 MHz, CDCl₃) δ 5.50 (ddt, J = 17.0, 10.1, 7.0 Hz, 1H), 5.21 (dq, J = 11.1, 1.4 Hz, 1H), 5.17 (dq, J = 4.0, 1.4 Hz, 1H), 3.17–3.02 (m, 3H), 2.86–2.76 (m, 2H), 2.62–2.47 (m, 2H), 2.16 (ddq, J = 14.0, 8.1, 7.0 Hz, 1H), 2.05 (ddq, J = 13.6, 8.1, 6.9 Hz, 1H), 1.92 (dt, J = 13.9, 7.0 Hz, 1H), 1.64 (sext, J = 7.6 Hz, 2H), 0.93 (t, J = 7.4 Hz, 3H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 202.7, 130.5, 120.6, 73.9, 51.5, 42.3, 36.8, 29.3, 17.8, 16.9, 13.5 ppm. IR: ν_max (neat) 2963, 2875, 1712 cm^–1. HRMS (APCI) m/z: calcd for C₁₁H₁₉O₃S [M + H]⁺ 231.1049, found 231.1040. HPLC: 74% ee (Chiralcel OD-H, hexane:i-PrOH = 95:5, flow rate = 1 mL/min, 30.0 °C, λ = 280 nm) t_R = 10.1 min (minor), t_R = 11.5 min (major). [α]: −59.0 (c = 0.25, CHCl₃).

(2R)-(2-Allyl-1,1-dioxo-thiolan-2-yl)(methyl)methanone (18u)

A vial was charged with 15u (55 mg, 0.22 mmol), [Pd₂dba₃] (10.0 mg, 11 μmol), L4 (23.2 mg, 29 μmol), and 1,4-dioxane (2.2 mL). The mixture was stirred at room temperature for 2 h and then concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 4:1] gave 18u (40 mg, 90%) as a yellow oil. R_f = 0.21 [petrol:EtOAc 4:1]. ¹H NMR (400 MHz, CDCl₃) δ 5.57–5.43 (m, 1H), 5.24–5.14 (m, 2H), 3.17–2.99 (m, 3H), 2.79 (dtd, J = 13.8, 6.9, 1.6 Hz, 1H), 2.57 (ddq, J = 15.0, 7.1, 1.5 Hz, 1H), 2.36 (s, 3H), 2.21–1.98 (m, 2H), 1.90 (dt, J = 14.0, 7.1 Hz, 1H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 200.5, 130.3, 120.6, 74.1, 51.5, 36.9, 29.2, 27.9, 17.8 ppm. IR: ν_max (neat) 3082, 2954, 1713 cm^–1. HRMS (APCI) m/z: calcd for C₉H₁₅O₃S [M + H]⁺ 203.0736, found 203.0737. HPLC: 21% ee (Chiralcel OD-H, hexane:i-PrOH = 95:5, flow rate = 1 mL/min, 30.0 °C, λ = 210 nm) t_R = 15.5 min (minor), t_R = 16.9 min (major). [α]: −23.2 (c = 0.35, CHCl₃).

(2R)-Phenyl-2-allyl-1,1-dioxo-thiane-2-carboxylate (19a)

A vial was charged with 16a (40 mg, 0.12 mmol), [Pd₂dba₃] (2.7 mg, 3.0 μmol), L4 (6.3 mg, 7.8 μmol), and 1,4-dioxane (1.2 mL). The mixture was stirred at room temperature for 2 h and then concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 4:1] gave 19a (34 mg, 96%) as a yellow oil. R_f = 0.21 [petrol:EtOAc 4:1]. ¹H NMR (300 MHz, CDCl₃) δ 7.40 (t, J = 8.0 Hz, 2H), 7.27 (tt, J = 7.6, 1.2 Hz, 1H), 7.11 (d, J = 7.4 Hz, 2H), 5.95 (dddd, J = 16.9, 10.0, 8.4, 6.2 Hz, 1H), 5.37–5.22 (m, 2H), 3.51–3.39 (m, 1H), 3.31 (ddt, J = 14.3, 6.3, 1.4 Hz, 1H), 3.12 (dt, J = 14.0, 5.2 Hz, 1H), 2.75 (dd, J = 14.3, 8.4 Hz, 1H), 2.45 (ddd, J = 14.8, 6.4, 3.5 Hz, 1H), 2.22–2.05 (m, 3H), 1.97–1.68 (m, 2H) ppm. ¹³C{¹H} NMR (75 MHz, CDCl₃): δ 166.9, 150.2, 130.8, 129.6, 126.5, 121.3, 120.8, 71.0, 50.4, 35.6, 33.1, 24.0, 20.3 ppm. IR: ν_max (neat) 3079, 2935, 2856, 1750 cm^–1. HRMS (APCI) m/z: calcd for C₁₅H₁₉O₄S [M + H]⁺ 295.0999, found 295.0985. HPLC: 64% ee (Chiralpak AD-H, hexane:i-PrOH = 90:10, flow rate = 1 mL/min, 30.0 °C, λ = 220 nm) t_R = 11.8 min (major), t_R = 14.5 min (minor). [α]: −55.0 (c = 0.25, CHCl₃).

(2R)-(4-Methoxyphenyl)-2-allyl-1,1-dioxo-thiane-2-carboxylate (19b)

A vial was charged with a 1:3.9 mixture of 25:16b (63.5 mg, corresponding to 55 mg of pure 16b, 0.15 mmol), [Pd₂dba₃] (3.5 mg, 3.75 μmol), L4 (8.0 mg, 9.75 μmol), and 1,4-dioxane (1.5 mL). The mixture was stirred at room temperature for 15 h and then concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 3:1] gave 19b (37 mg, 77%) as a colorless oil. R_f = 0.25 [petrol:EtOAc 2:1]. ¹H NMR (400 MHz, CDCl₃) δ 7.02 (d, J = 9.2 Hz, 2H), 6.89 (d, J = 9.1 Hz, 2H), 5.98–5.86 (m, 1H), 5.33–5.21 (m, 2H), 3.79 (s, 3H), 3.47–3.37 (m, 1H), 3.28 (ddt, J = 14.3, 6.2, 1.3 Hz, 1H), 3.14–3.06 (m, 1H), 2.73 (dd, J = 14.3, 8.4 Hz, 1H), 2.47–2.37 (m, 1H), 2.19–2.05 (m, 3H), 1.93–1.78 (m, 1H), 1.78–1.68 (m, 1H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 167.1, 157.7, 143.6, 130.8, 122.0, 120.6, 114.5, 70.9, 55.6, 50.3, 35.5, 32.9, 23.9, 20.2 ppm. IR: ν_max (neat) 2935, 1750, 1504 cm^–1. HRMS (ESI) m/z: calcd for C₁₅H₂₀NaO₅S [M + Na]⁺ 347.0924, found 347.0922. HPLC: 74% ee (Chiralpak AD-H, hexane:i-PrOH = 95:5, flow rate = 1 mL/min, 30.0 °C, λ = 220 nm) t_R = 34.0 min (major), t_R = 57.3 min (minor). [α]: −41.6 (c = 0.30, CHCl₃).

(2R)-Benzyl-2-allyl-1,1-dioxo-thiane-2-carboxylate (19c)

A vial was charged with 16c (53 mg, 0.15 mmol), [Pd₂dba₃] (6.9 mg, 7.5 μmol), L4 (15.9 mg, 19.5 μmol), and 1,4-dioxane (1.5 mL). The mixture was stirred at room temperature for 24 h and then concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 4:1] gave 19c (30.5 mg, 66%) as a colorless oil. R_f = 0.41 [petrol:EtOAc 2:1]. ¹H NMR (400 MHz, CDCl₃) δ 7.44–7.28 (m, 5H), 5.72 (dddd, J = 16.5, 10.1, 8.4, 6.2 Hz, 1H), 5.28 (d, J = 12.2 Hz, 1H), 5.23 (d, J = 12.2 Hz, 1H), 5.12 (dq, J = 9.4, 1.4 Hz, 1H), 5.10–5.05 (m, 1H), 3.36 (ddd, J = 14.4, 7.8, 5.8 Hz, 1H), 3.12 (ddt, J = 14.2, 6.3, 1.4 Hz, 1H), 3.04 (dt, J = 14.2, 5.4 Hz, 1H), 2.62 (dd, J = 14.2, 8.4 Hz, 1H), 2.32–2.23 (m, 1H), 2.09–2.00 (m, 3H), 1.74–1.57 (m, 2H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 167.7, 134.8, 130.8, 128.6, 128.5, 128.4, 120.2, 70.9, 67.9, 50.3, 35.5, 32.9, 23.9, 20.2 ppm. IR: ν_max (neat) 2924, 2853, 1731 cm^–1. HRMS (ESI) m/z: calcd for C₁₆H₂₁O₄S [M + H]⁺ 309.1155, found 309.1141. HPLC: 60% ee (Chiralpak AD-H, hexane:i-PrOH = 90:10, flow rate = 1 mL/min, 30.0 °C, λ = 220 nm) t_R = 13.8 min (major), t_R = 21.6 min (minor). [α]: −17.7 (c = 0.23, CHCl₃).

(2R)-(2-Allyl-1,1-dioxo-thian-2-yl)phenylmethanone (19d)

A vial was charged with 16d (48 mg, 0.15 mmol), [Pd₂dba₃] (6.9 mg, 7.5 μmol), L4 (15.9 mg, 19.5 μmol), and 1,4-dioxane (1.5 mL). The mixture was stirred at room temperature for 24 h and then concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 7:1] gave 19d (13 mg, 31%) as a colorless oil. R_f = 0.38 [petrol:EtOAc 2:1]. ¹H NMR (400 MHz, CDCl₃) δ 7.86 (dd, J = 8.5, 1.3 Hz, 2H), 7.53 (tt, J = 7.6, 1.2 Hz, 1H), 7.43 (t, J = 7.5 Hz, 2H), 5.54 (dddd, J = 17.0, 10.2, 8.4, 6.2 Hz, 1H), 5.02 (dq, J = 10.3, 1.3 Hz, 1H), 4.94 (dq, J = 16.9, 1.5 Hz, 1H), 3.48 (ddt, J = 15.1, 6.2, 1.5 Hz, 1H), 3.47–3.35 (m, 1H), 3.16 (dt, J = 14.3, 6.2 Hz, 1H), 2.84 (ddt, J = 15.1, 8.4, 1.1 Hz, 1H), 2.59 (ddd, J = 15.0, 8.2, 3.4 Hz, 1H), 2.18 (ddd, J = 14.7, 9.1, 3.2 Hz, 2H), 2.11 (quint, J = 6.0 Hz, 2H), 1.85–1.71 (m, 1H), 1.72–1.62 (m, 1H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 198.1, 138.2, 132.1, 130.3, 128.3, 128.3, 120.5, 76.0, 51.0, 36.0, 33.1, 24.0, 20.1 ppm. IR: ν_max (neat) 3069, 2935, 1671 cm^–1. HRMS (ESI) m/z: calcd for C₁₅H₁₉O₃S [M + H]⁺ 279.1049, found 279.1049. HPLC: 77% ee (Chiralcel OD-H, hexane:i-PrOH = 95:5, flow rate = 1 mL/min, 30.0 °C, λ = 240 nm) t_R = 25.9 min (major), t_R = 28.1 min (minor). [α]: −13.7 (c = 0.11, CHCl₃).

(2R)-(2-Allyl-1,1-dioxo-thian-2-yl)-(4-bromophenyl)methanone (19e)

A vial was charged with 16e (60 mg, 0.15 mmol), [Pd₂dba₃] (6.9 mg, 7.5 μmol), L4 (15.9 mg, 19.5 μmol), and 1,4-dioxane (1.5 mL). The mixture was stirred at room temperature for 15 h and then concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 6:1] gave 19e (44 mg, 82%) as a colorless oil. R_f = 0.38 [petrol:EtOAc 2:1]. ¹H NMR (400 MHz, CDCl₃) δ 7.79 (d, J = 8.8 Hz, 2H), 7.58 (d, J = 8.8 Hz, 2H), 5.47 (dddd, J = 17.0, 10.2, 8.3, 6.2 Hz, 1H), 5.05 (dq, J = 10.2, 1.3 Hz, 1H), 4.97 (dq, J = 16.9, 1.4 Hz, 1H), 3.45 (ddt, J = 15.0, 6.2, 1.6 Hz, 1H), 3.32 (dt, J = 14.3, 6.4 Hz, 1H), 3.17 (ddd, J = 14.4, 7.1, 6.0 Hz, 1H), 2.81 (ddt, J = 15.0, 8.3, 1.1 Hz, 1H), 2.56 (ddd, J = 15.0, 8.9, 3.4 Hz, 1H), 2.18–2.08 (m, 3H), 1.86–1.76 (m, 1H), 1.70–1.60 (m, 1H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 196.8, 136.8, 131.6, 130.2, 129.9, 127.3, 120.9, 75.8, 50.9, 35.8, 32.6, 23.9, 20.0 ppm. IR: ν_max (neat) 2935, 2864, 1675 cm^–1. HRMS (APCI) m/z: calcd for C₁₅H₁₆⁷⁹BrO₃S [M – H]⁻ 355.0009, found 355.0014. HPLC: 76% ee (Chiralpak AD-H, hexane:i-PrOH = 95:5, flow rate = 1 mL/min, 30.0 °C, λ = 254 nm) t_R = 27.5 min (major), t_R = 37.6 min (minor). [α]: −10.8 (c = 0.37, CHCl₃).

(2R)-(2-Allyl-1,1-dioxo-thian-2-yl)-(4-fluorophenyl)methanone (19f)

A vial was charged with 16f (51 mg, 0.15 mmol), [Pd₂dba₃] (6.9 mg, 7.5 μmol), L4 (15.9 mg, 19.5 μmol), and 1,4-dioxane (1.5 mL). The mixture was stirred at room temperature for 15 h and then concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 6:1] gave 19f (33 mg, 74%) as a colorless oil. R_f = 0.35 [petrol:EtOAc 2:1]. ¹H NMR (400 MHz, CDCl₃) δ 7.98 (dd, J = 9.0, 5.3 Hz, 2H), 7.11 (dd, J = 9.0, 8.3 Hz, 2H), 5.48 (dddd, J = 16.9, 10.1, 8.3, 6.1 Hz, 1H), 5.04 (dq, J = 10.2, 1.3 Hz, 1H), 4.95 (dq, J = 16.9, 1.5 Hz, 1H), 3.47 (ddt, J = 15.1, 6.3, 1.7 Hz, 1H), 3.34 (dt, J = 14.2, 6.4 Hz, 1H), 3.17 (dt, J = 14.2, 6.6 Hz, 1H), 2.83 (ddt, J = 15.0, 8.3, 1.1 Hz, 1H), 2.59 (ddd, J = 15.0, 8.8, 3.4 Hz, 1H), 2.21–2.08 (m, 3H), 1.87–1.76 (m, 1H), 1.71–1.60 (m, 1H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 195.9, 165.0 (d, J = 254.9 Hz), 134.1 (d, J = 3.3 Hz), 131.5 (d, J = 36.0 Hz), 130.0, 120.8, 115.5 (d, J = 21.8 Hz), 75.9, 50.9, 35.9, 32.8, 23.9, 20.0 ppm. ¹⁹F{¹H} NMR (376 MHz, CDCl₃): δ −105.4 ppm. IR: ν_max (neat) 3078, 2935, 1673 cm^–1. HRMS (APCI) m/z: calcd for C₁₅H₁₈FO₃S [M + H]⁺ 297.0955, found 297.0947. HPLC: 80% ee (Chiralcel OD-H, hexane:i-PrOH = 95:5, flow rate = 1 mL/min, 30.0 °C, λ = 254 nm) t_R = 19.0 min (major), t_R = 22.3 min (minor). [α]: −11.0 (c = 0.25, CHCl₃).

(2R)-(2-Allyl-1,1-dioxo-thian-2-yl)-(p-tolyl)methanone (19g)

A vial was charged with 16g (50.5 mg, 0.15 mmol), [Pd₂dba₃] (6.9 mg, 7.5 μmol), L4 (15.9 mg, 19.5 μmol), and 1,4-dioxane (1.5 mL). The mixture was stirred at room temperature for 15 h and then concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 6:1] gave 19g (19 mg, 43%) as a colorless solid. R_f = 0.51 [petrol:EtOAc 2:1]. m.p.: 70–71 °C. ¹H NMR (400 MHz, CDCl₃) δ 7.81 (d, J = 8.3 Hz, 2H), 7.23 (d, J = 7.9 Hz, 2H), 5.55 (dddd, J = 16.9, 10.2, 8.4, 6.1 Hz, 1H), 5.01 (dt, J = 10.4, 1.2 Hz, 1H), 4.95 (dq, J = 17.0, 1.5 Hz, 1H), 3.52–3.38 (m, 2H), 3.15 (ddd, J = 14.1, 6.7, 5.3 Hz, 1H), 2.85 (ddt, J = 15.3, 8.4, 1.1 Hz, 1H), 2.60 (ddd, J = 15.0, 7.8, 3.5 Hz, 1H), 2.40 (s, 3H), 2.18 (ddd, J = 15.0, 9.5, 3.4 Hz, 1H), 2.13–2.06 (m, 2H), 1.80–1.62 (m, 2H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 197.1, 143.2, 135.1, 130.5, 129.0, 128.8, 120.3, 76.2, 51.1, 36.0, 33.3, 24.0, 21.5, 20.2 ppm. IR: ν_max (neat) 2926, 1656 cm^–1. HRMS (APCI) m/z: calcd for C₁₆H₂₁O₃S [M + H]⁺ 293.1206, found 293.1192. HPLC: 80% ee (Chiralpak AD-H, hexane:i-PrOH = 95:5, flow rate = 1 mL/min, 30.0 °C, λ = 254 nm) t_R = 25.6 min (major), t_R = 31.3 min (minor). [α]: −20.6 (c = 0.17, CHCl₃).

(2R)-(2-Allyl-1,1-dioxo-thian-2-yl)-(4-methoxyphenyl)methanone (19h)

A vial was charged with a 1:8.1 mixture of 25:16h (57 mg, corresponding to 53 mg of pure 16h, 0.15 mmol), [Pd₂dba₃] (6.9 mg, 7.5 μmol), L4 (15.9 mg, 19.5 μmol), and 1,4-dioxane (1.5 mL). The mixture was stirred at room temperature for 15 h and then concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 2:1] gave 19h (23.5 mg, 51%) as a colorless oil. R_f = 0.55 [petrol:EtOAc 1:1]. ¹H NMR (400 MHz, CDCl₃) δ 8.00 (d, J = 9.1 Hz, 2H), 6.92 (d, J = 9.1 Hz, 2H), 5.55 (dddd, J = 17.0, 10.2, 8.4, 6.1 Hz, 1H), 5.00 (dq, J = 10.3, 1.3 Hz, 1H), 4.95 (dq, J = 16.9, 1.6 Hz, 1H), 3.87 (s, 3H), 3.50 (ddt, J = 15.3, 6.1, 1.5 Hz, 1H), 3.42 (ddd, J = 13.7, 7.9, 5.5 Hz, 1H), 3.14 (ddd, J = 14.2, 6.6, 4.9 Hz, 1H), 2.86 (ddt, J = 15.3, 8.5, 1.1 Hz, 1H), 2.62 (ddd, J = 15.0, 7.8, 3.4 Hz, 1H), 2.19 (ddd, J = 15.0, 9.5, 3.4 Hz, 1H), 2.14–2.04 (m, 2H), 1.81–1.60 (m, 2H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 195.0, 163.1, 131.6, 130.6, 130.0, 120.2, 113.5, 76.3, 55.5, 51.1, 36.1, 33.4, 24.0, 20.2 ppm. IR: ν_max (neat) 2935, 1697 cm^–1. HRMS (APCI) m/z: calcd for C₁₆H₂₁O₄S [M + H]⁺ 309.1155, found 309.1145. HPLC: 84% ee (Chiralpak AD-H, hexane:i-PrOH = 95:5, flow rate = 1 mL/min, 30.0 °C, λ = 280 nm) t_R = 44.9 min (major), t_R = 54.2 min (minor). [α]: +20.0 (c = 0.20, CHCl₃).

(2R)-(2-Allyl-1,1-dioxo-thian-2-yl)-(2-furyl)methanone (19i)

A vial was charged with a 1:6.8 mixture of 25:16i (52 mg, corresponding to 47 mg of pure 16i, 0.15 mmol), [Pd₂dba₃] (6.9 mg, 7.5 μmol), L4 (15.9 mg, 19.5 μmol), and 1,4-dioxane (1.5 mL). The mixture was stirred at room temperature for 15 h and then concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 3:1] gave 19i (32 mg, 80%) as a colorless oil. R_f = 0.41 [petrol:EtOAc 2:1]. ¹H NMR (400 MHz, CDCl₃) δ 7.60 (dd, J = 1.7, 0.8 Hz, 1H), 7.43 (dd, J = 3.6, 0.8 Hz, 1H), 6.56 (dd, J = 3.7, 1.7 Hz, 1H), 5.77 (dddd, J = 16.9, 10.2, 9.1, 5.7 Hz, 1H), 4.97–4.86 (m, 2H), 3.56–3.40 (m, 2H), 3.10 (dt, J = 14.1, 4.7 Hz, 1H), 3.01 (dd, J = 15.3, 9.1 Hz, 1H), 2.66 (dddd, J = 15.0, 6.0, 3.3, 1.4 Hz, 1H), 2.19 (ddd, J = 15.0, 11.8, 3.3 Hz, 1H), 2.10–1.98 (m, 2H), 1.72–1.62 (m, 1H), 1.60–1.48 (m, 1H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 184.0, 151.7, 146.2, 131.5, 120.8, 119.2, 112.6, 75.4, 51.2, 35.5, 33.3, 24.0, 20.5 ppm. IR: ν_max (neat) 2953, 1670 cm^–1. HRMS (APCI) m/z: calcd for C₁₃H₁₇O₄S [M + H]⁺ 269.0842, found 269.0829. HPLC: 90% ee (Chiralcel OD-H, hexane:i-PrOH = 95:5, flow rate = 1 mL/min, 30.0 °C, λ = 280 nm) t_R = 30.4 min (major), t_R = 37.0 min (minor). [α]: −4.1 (c = 0.25, CHCl₃).

(2R)-1-(2-allyl-1,1-dioxo-thian-2-yl)-2-methylpropan-1-one (19j)

A vial was charged with 16j (40 mg, 0.14 mmol), [Pd₂dba₃] (6.4 mg, 7.0 μmol), L4 (14.8 mg, 18.2 μmol), and 1,4-dioxane (1.4 mL). The mixture was stirred at room temperature for 2 h and then concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 4:1] gave 19j (32 mg, 94%) as a yellow oil. R_f = 0.22 [petrol:EtOAc 4:1]. ¹H NMR (300 MHz, CDCl₃) δ 5.50 (dddd, J = 17.0, 9.9, 8.5, 5.6 Hz, 1H), 5.26–5.13 (m, 2H), 3.48 (hept, J = 6.7 Hz, 1H), 3.29–3.00 (m, 3H), 2.74 (ddt, J = 15.1, 8.5, 1.1 Hz, 1H), 2.28 (ddd, J = 14.2, 10.0, 3.5 Hz, 1H), 2.13–2.00 (m, 3H), 1.79–1.66 (m, 1H), 1.64–1.49 (m, 1H), 1.15 (d, J = 6.6 Hz, 3H), 1.12 (d, J = 6.7 Hz, 3H) ppm. ¹³C{¹H} NMR (75 MHz, CDCl₃): δ 209.3, 130.2, 120.4, 75.6, 50.8, 37.3, 34.5, 29.7, 24.0, 20.4, 20.2, 19.7 ppm. IR: ν_max (neat) 2973, 2937, 2874, 1709 cm^–1. HRMS (APCI) m/z: calcd for C₁₂H₂₁O₃S [M + H]⁺ 245.1206, found 245.1208. HPLC: 88% ee (Chiralpak AD-H, hexane:i-PrOH = 90:10, flow rate = 1 mL/min, 30.0 °C, λ = 210 nm) t_R = 13.3 min (major), t_R = 14.4 min (minor). [α]: −168 (c = 0.20, CHCl₃).

(2R)-(2-Allyl-1,1-dioxo-thian-2-yl)cyclohexylmethanone (19k)

A vial was charged with 16k (49 mg, 0.15 mmol), [Pd₂dba₃] (6.9 mg, 7.5 μmol), L4 (15.9 mg, 19.5 μmol), and 1,4-dioxane (1.5 mL). The mixture was stirred at room temperature for 15 h and then concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 7:1] gave 19k (34 mg, 80%) as a colorless oil. R_f = 0.72 [petrol:EtOAc 4:1]. ¹H NMR (400 MHz, CDCl₃) δ 5.47 (dddd, J = 16.9, 10.0, 8.6, 5.5 Hz, 1H), 5.22–5.12 (m, 2H), 3.26–3.09 (m, 3H), 3.03 (dt, J = 14.3, 5.7 Hz, 1H), 2.72 (dd, J = 15.0, 8.6 Hz, 1H), 2.25 (ddd, J = 15.2, 9.9, 3.5 Hz, 1H), 2.09–1.98 (m, 3H), 1.98–1.88 (m, 1H), 1.79–1.63 (m, 5H), 1.60–1.49 (m, 1H), 1.44 (qd, J = 12.9, 3.4 Hz, 1H), 1.38–1.18 (m, 4H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 207.9, 130.4, 120.3, 75.4, 50.9, 47.9, 34.6, 30.1, 29.8, 29.7, 25.6, 25.5, 25.4, 24.0, 19.7 ppm. IR: ν_max (neat) 2927, 2855, 1701 cm^–1. HRMS (APCI) m/z: calcd for C₁₅H₂₅O₃S [M + H]⁺ 285.1519, found 285.1516. HPLC: 89% ee (Chiralcel OD-H, hexane:i-PrOH = 95:5, flow rate = 1 mL/min, 30.0 °C, λ = 210 nm) t_R = 9.2 min (major), t_R = 10.7 min (minor). [α]: −62.5 (c = 0.29, CHCl₃).

(2R)-(2-Allyl-1,1-dioxo-thian-2-yl)-tetrahydropyran-4-yl-methanone (19l)

A vial was charged with a 1:4.1 mixture of 25:16l (58 mg, corresponding to 49.5 mg of pure 16l, 0.15 mmol), [Pd₂dba₃] (6.9 mg, 7.5 μmol), L4 (15.9 mg, 19.5 μmol), and 1,4-dioxane (1.5 mL). The mixture was stirred at room temperature for 15 h and then concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 2:1] gave 19l (39 mg, 91%) as a colorless solid. R_f = 0.18 [petrol:EtOAc 2:1]. m.p.: 69–70 °C. ¹H NMR (400 MHz, CDCl₃) δ 5.41 (dddd, J = 16.9, 9.9, 8.3, 5.7 Hz, 1H), 5.24–5.13 (m, 2H), 3.97 (dt, J = 4.2, 2.0 Hz, 1H), 3.95 (dt, J = 4.3, 2.2 Hz, 1H), 3.49 (tt, J = 11.7, 3.8 Hz, 1H), 3.42 (tt, J = 11.9, 2.5 Hz, 2H), 3.27–3.09 (m, 2H), 2.99 (dt, J = 14.3, 4.9 Hz, 1H), 2.75 (dd, J = 15.1, 8.3 Hz, 1H), 2.25 (ddd, J = 14.5, 10.8, 3.3 Hz, 1H), 2.10–1.99 (m, 3H), 1.86 (dd, J = 13.3, 4.4 Hz, 1H), 1.80 (dd, J = 12.5, 4.1 Hz, 1H), 1.77–1.64 (m, 2H), 1.60–1.48 (m, 2H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 206.0, 129.9, 120.7, 75.5, 67.1, 66.8, 50.8, 45.0, 34.4, 29.7, 29.4, 29.3, 24.0, 19.6 ppm. IR: ν_max (neat) 2952, 2847, 1705 cm^–1. HRMS (APCI) m/z: calcd for C₁₄H₂₃O₄S [M + H]⁺ 287.1312, found 287.1306. HPLC: 91% ee (Chiralpak AD-H, hexane:i-PrOH = 95:5, flow rate = 1 mL/min, 30.0 °C, λ = 210 nm) t_R = 21.7 min (minor), t_R = 24.3 min (major). [α]: −73.0 (c = 0.34, CHCl₃).

(2R)-1-(2-Allyl-1,1-dioxo-thian-2-yl)ethanone (19n)

A vial was charged with 16n (40 mg, 0.15 mmol), [Pd₂dba₃] (6.9 mg, 7.5 μmol), L4 (15.9 mg, 19.5 μmol), and 1,4-dioxane (1.5 mL). The mixture was stirred at room temperature for 2 h and then concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 4:1] gave 19n (30 mg, 93%) as a yellow oil. R_f = 0.20 [petrol:EtOAc 4:1]. ¹H NMR (300 MHz, CDCl₃) δ 5.54 (dddd, J = 16.5, 9.9, 7.9, 6.5 Hz, 1H), 5.28–5.14 (m, 2H), 3.23–2.99 (m, 3H), 2.69 (ddt, J = 14.7, 7.9, 1.1 Hz, 1H), 2.43 (s, 3H), 2.30 (ddd, J = 14.9, 9.4, 3.6 Hz, 1H), 2.11–1.98 (m, 3H), 1.85–1.71 (m, 1H), 1.67–1.52 (m, 1H) ppm. ¹³C{¹H} NMR (75 MHz, CDCl₃): δ 201.6, 129.7, 120.7, 75.1, 50.5, 34.9, 30.0, 28.8, 24.0, 19.9 ppm. IR: ν_max (neat) 2941, 2868, 1709 cm^–1. HRMS (APCI) m/z: calcd for C₁₀H₁₇O₃S [M + H]⁺ 217.0893, found 217.0884. HPLC: 32% ee (Chiralcel OD-H, hexane:i-PrOH = 95:5, flow rate = 1 mL/min, 30.0 °C, λ = 210 nm) t_R = 16.3 min (major), t_R = 17.9 min (minor). [α]: −55.1 (c = 0.34, CHCl₃).

(2S)-4-tert-Butyl-2-phenyl-2-allyl-1,1-dioxo-1,4-thiazinane-2,4-dicarboxylate (20a)

A vial was charged with 17a (66 mg, 0.15 mmol), [Pd₂dba₃] (6.9 mg, 7.5 μmol), L4 (15.9 mg, 19.5 μmol), and 1,4-dioxane (1.5 mL). The mixture was stirred at room temperature for 15 h and then concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 4:1] gave 20a (50.5 mg, 85%) as a colorless oil. R_f = 0.43 [petrol:EtOAc 2:1]. ¹H NMR (400 MHz, DMSO-d₆, 130 °C) δ 7.45 (t, J = 7.8 Hz, 2H), 7.30 (t, J = 7.4 Hz, 1H), 7.15 (d, J = 8.1 Hz, 2H), 5.97 (ddt, J = 17.2, 10.1, 7.0 Hz, 1H), 5.35 (dq, J = 17.0, 1.5 Hz, 1H), 5.28 (dq, J = 10.1, 1.3 Hz, 1H), 4.20 (d, J = 14.9 Hz, 1H), 3.96 (d, J = 14.9 Hz, 1H), 3.90 (t, J = 5.6 Hz, 2H), 3.44 (qt, J = 14.3, 5.6 Hz, 2H), 3.06 (dd, J = 14.5, 7.1 Hz, 1H), 2.78 (tt, J = 7.5, 1.3 Hz, 1H), 1.44 (s, 9H) ppm. ¹³C{¹H} NMR (100 MHz, DMSO-d₆, 130 °C): δ 163.8, 152.8, 149.5, 129.8, 128.8, 125.7, 120.3, 119.7, 80.2, 70.5, 49.2, 47.5, 41.7, 32.3, 27.3 ppm. IR: ν_max (neat) 2978, 2931, 1751, 1695 cm^–1. HRMS (APCI) m/z: calcd for C₁₉H₂₅NNaO₆S [M + Na]⁺ 418.1295, found 418.1288. HPLC: 69% ee (Chiralpak AD-H, hexane:i-PrOH = 95:5, flow rate = 1 mL/min, 30.0 °C, λ = 204 nm) t_R = 17.1 min (major), t_R = 18.3 min (minor). [α]: −15.9 (c = 0.38, CHCl₃).

(2S)-2-Benzyl-4-tert-butyl-2-allyl-1,1-dioxo-1,4-thiazinane-2,4-dicarboxylate (20b)

A vial was charged with 17b (68 mg, 0.15 mmol), [Pd₂dba₃] (6.9 mg, 7.5 μmol), L4 (15.9 mg, 19.5 μmol), and 1,4-dioxane (1.5 mL). The mixture was stirred at room temperature for 15 h and then concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 4:1] gave 20b (51 mg, 83%) as a colorless oil. R_f = 0.62 [petrol:EtOAc 2:1]. ¹H NMR (400 MHz, DMSO-d₆, 130 °C) δ 7.42–7.34 (m, 5H), 5.77 (ddt, J = 17.2, 10.2, 7.1 Hz, 1H), 5.25–5.09 (m, 4H), 4.02 (d, J = 14.5 Hz, 1H), 3.90 (d, J = 14.5 Hz, 1H), 3.87–3.73 (m, 2H), 3.41–3.26 (m, 2H), 2.91 (dd, J = 14.6, 7.0 Hz, 1H), 2.65 (ddt, J = 14.5, 7.1, 1.3 Hz, 1H), 1.44 (s, 9H) ppm. ¹³C{¹H} NMR (100 MHz, DMSO-d₆, 130 °C): δ 164.8, 152.7, 134.4, 129.9, 127.7, 127.5, 127.2, 119.4, 80.1, 70.3, 66.9, 49.0, 47.5, 41.6, 32.3, 27.3 ppm. IR: ν_max (neat) 2976, 2931, 1735, 1697 cm^–1. HRMS (APCI) m/z: calcd for C₂₀H₂₇NNaO₆S [M + Na]⁺ 432.1451, found 432.1445. HPLC: 62% ee (Chiralpak AD-H, hexane:i-PrOH = 95:5, flow rate = 1 mL/min, 30.0 °C, λ = 204 nm) t_R = 18.8 min (major), t_R = 32.9 min (minor). [α]: −6.0 (c = 0.34, CHCl₃).

(2S)-tert-Butyl-2-allyl-2-benzoyl-1,1-dioxo-1,4-thiazinane-4-carboxylate (20c)

A vial was charged with 17c (63.5 mg, 0.15 mmol), [Pd₂dba₃] (6.9 mg, 7.5 μmol), L4 (15.9 mg, 19.5 μmol), and 1,4-dioxane (1.5 mL). The mixture was stirred at room temperature for 15 h and then concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 4:1] gave 20c (50 mg, 90%) as a colorless oil. R_f = 0.46 [petrol:EtOAc 2:1]. ¹H NMR (400 MHz, DMSO-d₆, 130 °C) δ 7.85 (dd, J = 8.4, 1.2 Hz, 2H), 7.59 (tt, J = 7.4, 1.4 Hz, 1H), 7.50 (t, J = 7.5 Hz, 2H), 5.61 (ddt, J = 17.3, 10.3, 7.0 Hz, 1H), 4.99 (dq, J = 10.3, 1.3 Hz, 1H), 4.93 (dq, J = 17.1, 1.6 Hz, 1H), 4.19 (d, J = 15.1 Hz, 1H), 4.08 (dd, J = 15.1, 1.4 Hz, 1H), 3.97 (dddd, J = 14.4, 6.7, 4.2, 1.5 Hz, 1H), 3.76 (ddd, J = 14.1, 8.2, 3.7 Hz, 1H), 3.51–3.36 (m, 2H), 3.22 (ddq, J = 15.4, 7.2, 1.2 Hz, 1H), 2.89 (ddt, J = 15.3, 6.8, 1.4 Hz, 1H), 1.38 (s, 9H) ppm. ¹³C{¹H} NMR (100 MHz, DMSO-d₆, 130 °C): δ 195.0, 152.8, 137.5, 131.6, 129.6, 127.5, 127.5, 119.4, 80.1, 75.5, 49.8, 48.1, 41.6, 32.8, 27.2 ppm. IR: ν_max (neat) 2980, 2931, 1695, 1673 cm^–1. HRMS (ESI) m/z: calcd for C₁₉H₂₅NNaO₅S [M + Na]⁺ 402.1346, found 402.1349. HPLC: 86% ee (Chiralcel OD-H, hexane:i-PrOH = 95:5, flow rate = 1 mL/min, 30.0 °C, λ = 210 nm) t_R = 22.9 min (major), t_R = 30.2 min (minor). [α]: −32.8 (c = 0.43, CHCl₃).

(2S)-tert-Butyl-2-allyl-2-(2-methylpropanoyl)-1,1-dioxo-1,4-thiazinane-4-carboxylate (20d)

A vial was charged with 17d (58.5 mg, 0.15 mmol), [Pd₂dba₃] (6.9 mg, 7.5 μmol), L4 (15.9 mg, 19.5 μmol), and 1,4-dioxane (1.5 mL). The mixture was stirred at room temperature for 15 h and then concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 6:1] gave 20d (47 mg, 91%) as a colorless oil. R_f = 0.56 [petrol:EtOAc 2:1]. ¹H NMR (400 MHz, DMSO-d₆, 130 °C) δ 5.69 (dddd, J = 16.8, 10.2, 7.5, 6.4 Hz, 1H), 5.25 (dq, J = 17.0, 1.6 Hz, 1H), 5.19 (dq, J = 10.2, 1.4 Hz, 1H), 4.23 (dd, J = 14.9, 2.2 Hz, 1H), 4.21–4.14 (m, 1H), 3.70 (dd, J = 14.9, 1.3 Hz, 1H), 3.50–3.37 (m, 2H), 3.30 (hept, J = 6.7 Hz, 1H), 3.23–3.16 (m, 1H), 3.05 (ddq, J = 15.1, 7.4, 1.3 Hz, 1H), 2.77 (ddt, J = 15.1, 6.4, 1.6 Hz, 1H), 1.45 (s, 9H), 1.07 (d, J = 6.6 Hz, 3H), 1.07 (d, J = 1.5 Hz, 3H) ppm. ¹³C{¹H} NMR (100 MHz, DMSO-d₆, 130 °C): δ 206.6, 152.9, 129.9, 119.5, 80.0, 75.1, 49.0, 46.1, 41.6, 36.8, 32.4, 27.3, 18.7, 18.6 ppm. IR: ν_max (neat) 2978, 2931, 1695 cm^–1. HRMS (ESI) m/z: calcd for C₁₆H₂₇NNaO₅S [M + Na]⁺ 368.1502, found 368.1491. HPLC: 85% ee (Chiralpak AD-H, hexane:i-PrOH = 95:5, flow rate = 1 mL/min, 30.0 °C, λ = 210 nm) t_R = 8.0 min (major), t_R = 10.1 min (minor). [α]: −18.3 (c = 0.38, CHCl₃).

Synthesis of Allyl Enol Carbonates 27

1-((2Z)-1,1-Dioxo-thiolan-2-ylidene)-2-methylpropylprop-2-en-1-yl Carbonate ((E)-27) and 1-((2E)-1,1-Dioxo-thiolan-2-ylidene)-2-methylpropylprop-2-en-1-yl Carbonate ((Z)-27)

A solution of 34(29) (234 mg, 1.23 mmol) in THF (20 mL) was cooled to −78 °C. NaHMDS (1 M in THF, 1.48 mL, 1.48 mmol) was added dropwise, and the mixture was stirred at −78 °C for 30 min. Allyl chloroformate (0.157 mL, 1.48 mmol) was added dropwise. The mixture was allowed to warm to room temperature and stirred for 15 h. The reaction was quenched with aq. HCl (1 N, 10 mL) and diluted with water (10 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (100 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [6:1–5:1–2:1 heptane:EtOAc] gave (E)-27 (82 mg, 24%) as a colorless oil and (Z)-27 (59 mg, 18%) as a colorless oil.

Isomer (E)-27. R_f = 0.33 [petrol:EtOAc 2:1]. ¹H NMR (400 MHz, CDCl₃) δ 5.95 (ddt, J = 17.1, 10.4, 5.8 Hz, 1H), 5.41 (dq, J = 17.2, 1.4 Hz, 1H), 5.33 (dq, J = 10.4, 1.2 Hz, 1H), 4.69 (dt, J = 5.8, 1.3 Hz, 2H), 3.42 (hept, J = 6.8 Hz, 1H), 3.12 (t, J = 7.1 Hz, 2H), 2.63 (t, J = 7.0 Hz, 2H), 2.15 (quint, J = 7.0 Hz, 2H), 1.13 (d, J = 6.8 Hz, 6H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 157.3, 150.8, 130.7, 128.5, 119.8, 69.5, 52.3, 30.6, 25.6, 18.9, 18.8 ppm. IR: ν_max (neat) 2974, 2939, 1761, 1675 cm^–1. HRMS (APCI) m/z: calcd for C₁₂H₁₈NO₅S [M + NH₄]⁺ 292.1213, found 292.1205.

Isomer (Z)-27. R_f = 0.11 [petrol:EtOAc 2:1]. ¹H NMR (400 MHz, CDCl₃) δ 5.97 (ddt, J = 17.2, 10.5, 5.8 Hz, 1H), 5.41 (dq, J = 17.2, 1.5 Hz, 1H), 5.29 (dq, J = 10.4, 1.2 Hz, 1H), 4.72 (dt, J = 5.8, 1.4 Hz, 2H), 3.06 (t, J = 7.1 Hz, 2H), 2.79 (t, J = 7.0 Hz, 2H), 2.67 (hept, J = 7.0 Hz, 1H), 2.21 (quint, J = 7.1 Hz, 2H), 1.16 (d, J = 7.0 Hz, 6H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 155.8, 152.3, 131.1, 126.9, 119.2, 69.6, 51.3, 32.5, 24.8, 19.0, 18.8 ppm. IR: ν_max (neat) 2924, 2853, 1766, 1673 cm^–1. HRMS (ESI) m/z: calcd for C₁₂H₁₈NaO₅S [M + Na]⁺ 297.0767, found 297.0764.

Synthesis of Deuterium-Labeled Substrates

3-Trimethylsilylprop-2-ynylimidazole-1-carboxylate (35)

A solution of 1,1′-carbonyldiimidazole (8.51 g, 52.5 mmol) in THF (200 mL) was cooled to 0 °C. (3-Trimethylsilyl)propargyl alcohol (5.18 mL, 35 mmol) was added dropwise. The reaction mixture was stirred at 0 °C for 2 h. The mixture was allowed to warm to room temperature and concentrated under reduced pressure. Purification by flash column chromatography [petrol:EtOAc 9:1–4:1] gave 35 (3.35 g, 43%) as a colorless oil. R_f = 0.32 [petrol:EtOAc 2:1]. ¹H NMR (400 MHz, CDCl₃) δ 8.18 (t, J = 1.1 Hz, 1H), 7.46 (t, J = 1.5 Hz, 1H), 7.08 (dd, J = 1.7, 0.8 Hz, 1H), 4.99 (s, 2H), 0.20 (s, 9H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 148.0, 137.2, 130.7, 117.2, 96.7, 94.5, 56.1, −0.5 ppm. IR: ν_max (neat) 2961, 2902, 2186, 1763 cm^–1. HRMS (APCI) m/z: calcd for C₁₀H₁₅N₂O₂Si [M + H]⁺ 223.0897, found 223.0890.

3-Trimethylsilylprop-2-ynyl-1,1-dioxothiolane-2-carboxylate (36)

A solution of sulfolane (21, 418 mg, 3.48 mmol) in THF (25 mL) was cooled to −78 °C. LiHMDS (1 M in THF, 7.31 mL, 7.31 mmol) was added dropwise. The solution was stirred at −78 °C for 1 h. The mixture was allowed to warm to room temperature, and a solution of 35 (850 mg, 3.83 mmol) in THF (10 mL) was added dropwise. The mixture was stirred at room temperature for 1 h. The reaction was quenched with aq. HCl (1 N, 50 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (100 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 9:1–4:1] gave 36 (538 mg, 56%) as a colorless solid. R_f = 0.29 [petrol:EtOAc 2:1]. m.p.: 105–106 °C. ¹H NMR (400 MHz, CDCl₃): δ 4.92 (d, J = 15.8 Hz, 1H), 4.70 (d, J = 15.8 Hz, 1H), 3.96 (t, J = 7.6 Hz, 1H), 3.19–3.05 (m, 2H), 2.62–2.50 (m, 1H), 2.46–2.31 (m, 2H), 2.23–2.10 (m, 1H), 0.17 (s, 9H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 164.9, 97.7, 93.2, 64.4, 54.5, 51.5, 26.0, 20.4, −0.4 ppm. IR: ν_max (neat) 2965, 2902, 2190, 1739 cm^–1. HRMS (APCI) m/z: calcd for C₁₁H₁₉O₄SSi [M + H]⁺ 275.0768, found 275.0767.

2-(3-Trimethylsilylprop-2-ynyl)-2-tolyl dihydrothiophene-2,2(3H)-dicarboxylate 1,1-dioxide (37)

36 (588 mg, 2.15 mmol) was dissolved in THF (25 mL). NaHMDS (1 M in THF, 2.37 mL, 2.37 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. p-Tolyl chloroformate (0.34 mL, 2.37 mmol) was added dropwise, and the mixture was stirred for 5 h. The reaction was quenched with aq. HCl (1 N, 25 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (100 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 9:1–6:1] gave 37 (538 mg, 61%) as a colorless oil. R_f = 0.61 [petrol:EtOAc 2:1]. ¹H NMR (400 MHz, CDCl₃): δ 7.18 (d, J = 8.4 Hz, 2H), 7.08 (d, J = 8.5 Hz, 2H), 4.94 (d, J = 15.7 Hz, 1H), 4.89 (d, J = 15.7 Hz, 1H), 3.49–3.31 (m, 2H), 2.94 (dt, J = 14.9, 7.6 Hz, 1H), 2.75 (dt, J = 14.5, 7.4 Hz, 1H), 2.38–2.27 (m, 5H), 0.16 (s, 9H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 163.9, 162.8, 148.1, 136.4, 130.0, 120.9, 97.1, 93.9, 74.8, 55.3, 50.6, 30.2, 20.9, 17.2, −0.5 ppm. IR: ν_max (neat) 3034, 2960, 2193, 1746 cm^–1. HRMS (APCI) m/z: calcd for C₁₉H₂₅O₆SSi [M + H]⁺ 409.1136, found 409.1126.

3-Trimethylsilylprop-2-ynyl-2-(4-methylbenzoyl)-1,1-dioxo-thiolane-2-carboxylate (38)

36 (533 mg, 1.95 mmol) was dissolved in THF (20 mL). NaHMDS (1 M in THF, 2.14 mL, 2.14 mmol) was added dropwise. The solution was stirred at room temperature for 30 min. p-Toluoyl chloride (0.283 mL, 2.14 mmol) was added dropwise, and the mixture was heated at 80 °C for 15 h. The reaction was quenched with aq. HCl (1 N, 25 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (100 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 9:1–4:1] gave 38 (577 mg, 75%) as a colorless oil. R_f = 0.52 [petrol:EtOAc 2:1]. ¹H NMR (400 MHz, CDCl₃): δ 7.88 (d, J = 8.4 Hz, 2H), 7.26 (d, J = 7.9 Hz, 2H), 4.78 (d, J = 15.6 Hz, 1H), 4.71 (d, J = 15.6 Hz, 1H), 3.46 (ddd, J = 13.0, 9.0, 6.7 Hz, 1H), 3.35 (ddd, J = 13.0, 8.6, 6.1 Hz, 1H), 3.20 (dt, J = 14.4, 7.7 Hz, 1H), 2.65 (ddd, J = 14.1, 7.4, 6.5 Hz, 1H), 2.40 (s, 3H), 2.38–2.19 (m, 2H), 0.12 (s, 9H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 186.6, 165.8, 145.0, 132.5, 129.4, 129.4, 96.9, 93.4, 77.4, 54.6, 51.9, 32.0, 21.7, 17.5, −0.5 ppm. IR: ν_max (neat) 2957, 2917, 2849, 2186, 1740, 1683 cm^–1. HRMS (APCI) m/z: calcd for C₁₉H₂₅O₅SSi [M + H]⁺ 393.1186, found 393.1170.

2-(3-²H-Prop-2-ynyl)-2-tolyldihydrothiophene-2,2(3H)-dicarboxylate 1,1-dioxide ([D]-39)

37 (414 mg, 1.01 mmol) was dissolved in THF (15 mL). Deuterium oxide (5 mL) was added followed by tetrabutylammonium fluoride (1 M in THF, 1.12 mL, 1.12 mmol), and the reaction mixture was stirred at room temperature for 2 h. The solution was diluted with water (20 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (100 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 6:1–4:1] gave [D]-39 (304 mg, 89%, 95% D) as a pale yellow solid. R_f = 0.32 [petrol:EtOAc 2:1]. m.p.: 97–98 °C. ¹H NMR (400 MHz, CDCl₃): δ 7.19 (d, J = 8.4 Hz, 2H), 7.08 (d, J = 8.5 Hz, 2H), 4.95 (d, J = 15.5 Hz, 1H), 4.89 (d, J = 15.4 Hz, 1H), 3.49–3.33 (m, 2H), 2.93 (dt, J = 14.8, 7.4 Hz, 1H), 2.79 (dt, J = 14.5, 7.3 Hz, 1H), 2.55 (t, J = 2.5 Hz, 0.05H), 2.38–2.29 (m, 5H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 163.8, 162.8, 148.1, 136.4, 130.0, 120.8, 74.9, 54.5, 50.7, 30.2, 20.9, 17.3 ppm; two alkyne carbon signals were not observed. IR: ν_max (neat) 3017, 2965, 2918, 2850, 2579, 1984, 1767, 1743 cm^–1. HRMS (APCI) m/z: calcd for C₁₆H₁₆DO₆S [M + H]⁺ 338.0803, found 338.0794.

(3-²H-Prop-2-ynyl)-2-(4-methylbenzoyl)-1,1-dioxo-thiolane-2-carboxylate ([D]-40)

38 (517 mg, 1.32 mmol) was dissolved in THF (15 mL). Deuterium oxide (5 mL) was added followed by tetrabutylammonium fluoride (1 M in THF, 1.98 mL, 1.98 mmol), and the reaction mixture was stirred at room temperature for 6 h. The solution was diluted with water (20 mL). The mixture was extracted with EtOAc (3 × 50 mL), washed with brine (100 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 6:1] gave [D]-40 (343 mg, 81%, 98% D) as a colorless solid. R_f = 0.24 [petrol:EtOAc 2:1]. m.p.: 143–144 °C. ¹H NMR (400 MHz, CDCl₃): δ 7.86 (d, J = 8.3 Hz, 2H), 7.26 (d, J = 7.9 Hz, 2H), 4.78 (d, J = 15.4 Hz, 1H), 4.68 (d, J = 15.4 Hz, 1H), 3.50–3.32 (m, 2H), 3.18 (dt, J = 14.8, 7.6 Hz, 1H), 2.69 (ddd, J = 14.2, 7.4, 6.4 Hz, 1H), 2.53 (t, J = 2.4 Hz, 0.01H), 2.40 (s, 3H), 2.37–2.20 (m, 2H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 186.9, 165.8, 145.1, 132.6, 129.4, 129.3, 77.4, 53.9, 51.8, 31.9, 21.7, 17.6 ppm; two alkyne carbon signals were not observed. IR: ν_max (neat) 3013, 2958, 2920, 2578, 1981, 1744, 1677 cm^–1. HRMS (APCI) m/z: calcd for C₁₆H₁₆DO₅S [M + H]⁺ 322.0854, found 322.0838.

2-(3-²H-Allyl)-2-tolyl-dihydrothiophene-2,2(3H)-dicarboxylate-1,1-dioxide ([D]-15d)

A suspension of [D]-39 (194 mg, 0.58 mmol), Pd/CaCO₃ (19.4 mg), and quinoline (0.136 mL, 1.15 mmol) in EtOAc (11.5 mL) was degassed with argon. The mixture was cooled to 0 °C and then stirred at 0 °C under a hydrogen atmosphere for 20 min. The suspension was filtered through a pad of Celite, washed with aq. HCl (1 N, 15 mL) and brine (15 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 9:1] gave [D]-15d (160 mg, 82%, 93% D) as a colorless solid. R_f = 0.32 [petrol:EtOAc 2:1]. m.p.: 60–61 °C. ¹H NMR (400 MHz, CDCl₃): δ 7.18 (d, J = 8.1 Hz, 2H), 7.05 (d, J = 8.5 Hz, 2H), 6.02–5.90 (m, 1H), 5.44 (ddt, J = 17.2, 4.9, 1.4 Hz, 0.25H), 5.34–5.28 (m, 0.82H), 4.83 (dt, J = 5.9, 1.3 Hz, 2H), 3.47–3.33 (m, 2H), 2.91 (dt, J = 14.9, 7.6 Hz, 1H), 2.79 (dt, J = 14.5, 7.4 Hz, 1H), 2.36–2.28 (m, 5H) ppm. ¹³C{¹H} NMR (100 MHz, CDCl₃): δ 164.2, 163.1, 148.1, 136.4, 130.4, 130.0, 120.8, 119.5 (t, J = 24.1 Hz), 75.0, 67.7, 50.5, 30.2, 20.8, 17.3 ppm. IR: ν_max (neat) 3034, 2954, 1735 cm^–1. HRMS (APCI) m/z: calcd for C₁₆H₁₈DO₆S [M + H]⁺ 340.0960, found 340.0947.

(3-²H-Allyl)-2-(4-methylbenzoyl)-1,1-dioxo-thiolane-2-carboxylate ([D]-15l)

A suspension of [D]-40 (212 mg, 0.66 mmol), Pd/CaCO₃ (21.2 mg), and quinoline (0.156 mL, 1.32 mmol) in EtOAc (13 mL) was degassed with argon. The mixture was stirred at room temperature under a hydrogen atmosphere for 15 min. The suspension was filtered through a pad of Celite, washed with aq. HCl (1 N, 15 mL) and brine (15 mL), dried (MgSO₄), and concentrated under reduced pressure. Purification by flash column chromatography [hexane:EtOAc 9:1–6:1] gave [D]-15l (152 mg, 71%, 93% D) as a colorless solid. R_f = 0.34 [petrol:EtOAc 2:1]. m.p.: 68–69 °C. ¹H NMR (300 MHz, CDCl₃): δ 7.85 (d, J = 8.5 Hz, 2H), 7.25 (d, J = 8.5 Hz, 2H), 5.75–5.59 (m, 1H), 5.23–5.09 (m, 1.07H), 4.63 (dd, J = 5.9, 1.2 Hz, 2H), 3.40 (qdd, J = 13.0, 8.7, 6.6 Hz, 2H), 3.13 (dt, J = 14.7, 7.5 Hz, 1H), 2.70 (dt, J = 14.2, 7.0 Hz, 1H), 2.40 (s, 3H), 2.38–2.16 (m, 2H) ppm. ¹³C{¹H} NMR (75 MHz, CDCl₃): δ 187.5, 166.2, 144.9, 132.8, 130.1, 129.4, 129.2, 119.6 (t, J = 24.6 Hz), 77.7, 67.2, 51.7, 31.9, 21.7, 17.6 ppm. IR: ν_max (neat) 3050, 3017, 2999, 2953, 1733, 1675 cm^–1. HRMS (APCI) m/z: calcd for C₁₆H₁₈DO₅S [M + H]⁺ 324.1010, found 324.0997.

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.joc.2c01240.

• Copies of NMR spectra of all new compounds, HPLC traces for ee determination, X-ray data for 18b, and details of the mechanistic study (PDF)

The authors declare no competing financial interest.