Palladium-Catalyzed C2-Selective Oxidative Olefination of Benzo[b]thiophene 1,1-Dioxides with Styrenes and Acrylates

Bingbin Yang; Yaoyao Lu; Luqiong Duan; Xiaoyu Ma; Yaolin Xia; Xiaolei Huang

doi:10.1021/acsomega.2c07427

. 2023 Mar 10;8(11):10100–10110. doi: 10.1021/acsomega.2c07427

Palladium-Catalyzed C2-Selective Oxidative Olefination of Benzo[b]thiophene 1,1-Dioxides with Styrenes and Acrylates

Bingbin Yang ¹, Yaoyao Lu ¹, Luqiong Duan ¹, Xiaoyu Ma ¹, Yaolin Xia ¹, Xiaolei Huang ^1,^*

PMCID: PMC10034782 PMID: 36969423

Abstract

Here, we disclose a novel Pd(II)-catalyzed oxidative Heck reaction of benzo[b]thiophene 1,1-dioxides with styrenes and acrylates. This transformation features broad functional group tolerance and high C2 selectivity. Furthermore, the photoluminescence properties of C-2 alkenylated products have been characterized, which illustrates the potential usefulness of our protocol in constructing π-conjugated fluorescent molecules.

Introduction

Thiophenes are the most popular structural motifs of luminescent materials for optoelectronic devices due to the rich Π-electrons and high aromaticity.¹ Thiophene 1,1-dioxide is a good electron-withdrawing group, which has been introduced into thiophene-based materials to improve photophysical properties.² For example, Barbarella and co-workers first demonstrated that oxidizing conjugated oligothiophenes to thiophene 1,1-dioxides will reduce the highest occupied molecular orbital–least unoccupied molecular orbital (HOMO–LUMO) band gap value and enhance photoluminescence efficiency.^3,4 Dibenzothiophene 1,1-dioxide unit was incorporated into the chain of oligofluorenes, showing high luminescence efficiency,^5a strong solvatochromism,^5b and dual fluorescence.^5c 2,3-Diaryl-substituted benzo[b]thiophene 1,1-dioxides represented a new aggregation-induced emission platform.⁶ Thus, the synthesis and modification of various thiophene 1,1-dioxides have attracted significant attention of synthetic chemists.

Traditional methods for the synthesis of thiophene 1,1-dioxides contain oxidation of thiophenes,^6,7 Diels–Alder reactions,⁸ and C–X/C–M (M = Sn and B) cross-couplings.⁹ Recently, transition-metal-catalyzed oxidative C–H activation has been one of the most powerful tools in organic synthesis.¹⁰ However, catalytic functionalization of thiophene 1,1-dioxides via C–H activation strategy is highly rare. Nelson¹¹ and Farinola¹² reported Cu- and Pd-catalyzed C–H activation/arylation of benzodithiophene S,S-tetraoxides with aryl iodides for the preparation of extended heteroaromatic conjugated molecules, respectively (Scheme 1a). In 2019, N-chelator-directed diastereoselective oxidative annulation of benzo[b]thiophene 1,1-dioxides with amino quinolinamides via double C–H activation was developed by Nicholls and co-workers (Scheme 1b).¹³ Very recently, Parthasarathy achieved N-pyridinyl-assisted oxidative cross-dehydrogenative coupling of N-pyridinylindoles with benzo[b]thiophene 1,1-dioxides (Scheme 1c).¹⁴ Herein, we would like to report a novel palladium-catalyzed C2-selective oxidative olefination of benzo[b]thiophene 1,1-dioxides with alkenes (Scheme 1d).

Results and Discussion

Our study commenced with the oxidative Heck reaction of benzo[b]thiophene 1,1-dioxide 1a with styrene 2a as the model reaction to optimize the reaction conditions. Initially, (E)-2-styrylbenzo[b]thiophene 1,1-dioxide 3a was generated in 37% yield in the presence of 5 mol % of Pd(OAc)₂ and 3.0 equiv of AgOAc using 1.0 mL of AcOH as the solvent at 100 °C for 24 h (Table S1, entry 1). At the same time, a trace amount of homo-coupling product from benzo[b]thiophene 1,1-dioxide 1a and nonisolated complex mixture was obtained as byproducts. Compound 3a was further testified by X-ray crystallographic analysis.¹⁵ Other Pd(II) catalysts such as PdCl₂ and Pd(TFA)₂ gave lower yields (Table S1, entries 2 and 3). Among various oxidants including Ag(I) salts, Cu(OAc)₂, K₂S₂O₈, and BQ examined, AgOAc was the most effective (Table S1, entries 4–8). Using PivOH instead of AcOH, the yield of 3a was increased to 71% (Table S1, entries 9–11). Further screenings showed that 3a can be obtained in 87% yield in the presence of 2 mL of PivOH as solvent at 80 °C (Table S1, entries 12–17). The addition of a great quantity of acid brought trouble to post-processing. To our delight, the oxidative Heck reaction could occur with 5 equiv of PivOH in some common solvents (Table 1). Among various solvents examined, tetrahydrofuran (THF) was superior to toluene, 1,2-dichloroethane, 1,4-dioxane, DMSO, DMF, isopropanol, and methyl tert-butyl ether (Table 1, entries 1–8). This transformation afforded 3a in 88% yield when AgOAc was changed to AgOPiv (Table 1, entry 9). Further optimization decreased the amount of PivOH to 3.0 equiv with a lower temperature (Table 1, entries 10 and 11). When the amount of PivOH was further decreased to 1.0 equiv, only 65% yield of 3a was obtained (Table 1, entry 12). The result indicated that redundant AgOPiv might assist in accelerating the metalation process.^10d In addition, 15% yield of 3a was obtained, when benzo[b]thiophene 1,1-dioxide 1a reacted with styrene 2a under the reported condition of the Heck reaction of thiophenes.¹⁶ Finally, the yield of 3a can reach 95% under the optimized reaction condition comprising Pd(OAc)₂ (5 mol %), AgOPiv (3.0 equiv), and PivOH (3.0 equiv) in THF solution at 80 °C for 12 h.

Table 1. Optimization of Pd(II)-Catalyzed Oxidative Heck Reaction^a.

entry	Ag salt	solvent	x	yield (%)^b
1	AgOAc	toluene	5.0	45
2	AgOAc	DCE	5.0	71
3	AgOAc	1,4-dioxane	5.0	63
4	AgOAc	DMSO	5.0	nr
5	AgOAc	IPA	5.0	nr
6	AgOAc	DMF	5.0	34
7	AgOAc	THF	5.0	78
8	AgOAc	MTBE	5.0	22
9	AgOPiv	THF	5.0	88
10	AgOPiv	THF	3.0	92
11^c	AgOPiv	THF	3.0	95
12	AgOPiv	THF	1.0	65

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Reaction conditions: 1a (0.1 mmol), styrene 2a (0.15 mmol, 1.5 equiv), Pd(OAc)₂ (5 mol %), Ag salt (3.0 equiv), and PivOH (x equiv) in solvent (0.6 mL) at 120 °C for 12 h.

GC yields.

At 80 °C. DCE = 1,2-dichloroethane, DMSO = dimethyl sulfoxide, IPA = isopropanol, DMF = N,N-dimethylformamide, THF = tetrahydrofuran, MTBE = methyl tert-butyl ether.

With the optimal conditions in hand, we next investigated the scope of this oxidative Heck reaction. As summarized in Scheme 2, various styrene derivatives possessing electron-donating groups such as methyl, methoxy, tert-butyl, and acetoxyl on the aryl moiety smoothly coupled with benzo[b]thiophene 1,1-dioxide 1a, affording the desired products in good to excellent yields (3b–3h). 1-Methyl-2-vinylbenzene reacted with 1a to give the corresponding alkenylated products in only 44% yield (3d), which implied that steric effect diminishes the reactivity of styrenes. Styrenes with electron-withdrawing substituents (halide, trifluoromethyl, and ester groups) can be also tolerated in the oxidative Heck reaction, but only moderate yields were obtained (3i–3l). Moreover, 2-vinylnaphthalene underwent this transformation in 61% yield (3m). Acrylates were investigated under standard conditions, and the desired products were obtained in moderate yields (3n and 3o). It is worth noting that aliphatic olefins, cyclic alkenes, and α- or β-substituted styrenes were limited in the oxidative Heck transformation, and extremely complex mixtures were obtained as a result.

Subsequently, the scope of benzo[b]thiophene 1,1-dioxide derivatives was examined. Benzo[b]thiophene 1,1-dioxides with various substituents were compatible with this palladium-catalyzed oxidative Heck reaction in good to excellent yields (Scheme 3). 3-Methylbenzo[b]thiophene 1,1-dioxide reacted with 2a to afford the desired product in satisfactory yields, which revealed that steric effect had no obvious influence on the reactivity of the benzo[b]thiophene 1,1-dioxides (4a and 4d). Bis sulfone substrate was investigated with 3.0 equiv of styrene 2a, and bis alkenylated product 4h was obtained in 78% yield. This result showed a positive outlook of this oxidative Heck reaction in the synthesis of new functional materials because both the bis thiophenes and bis sulfones are core skeletons in numerous photoelectric material molecules. A great deal of effort tried to realize the olefination of thiophene 1,1-dioxide. However, thiophene 1,1-dioxides were instable even at <−40 °C and can be easily transformed to dimers along with the liberation of SO₂.¹⁷

Scheme 3 — Reactions were performed with benzo[b]thiophene 1,1-dioxides 1 (0.20 mmol), and styrene 2a (0.30 mmol) in 1.2 mL of THF.

Yields of isolated products.

2a (0.6 mmol) was used.

Next, the gram-scale reaction of benzo[b]thiophene 1,1-dioxide 1a with styrene 2a was carried out under standard conditions to assess the practical synthetic utility of this oxidative olefination method (Scheme 4). The desired product 3a was isolated in up to 86% yield from the scale-up reaction.

To evaluate the potential usefulness of our protocol in constructing thiophene 1,1-dioxides-alkenes-type π-conjugated skeletons for the screening of fluorescent molecules, we characterized the photophysical properties of several alkenylated products. As shown in Figure 1a, ultraviolet–visible (UV–vis) spectra of 3a, 3f, and 3g in dichloromethane solutions gave the absorption maxima from 363 to 389 nm. The absorption spectra of bis alkenylated product 4h are red-shifted obviously due to the expansion of π-conjugated system and the introduction of electron-donating alkoxy group. In addition, all of the products exhibited significant fluorescence emission in both DCM solution and the solid state (Figure 1b–d).

(a, b) Absorption and emission spectra, respectively. (c, d) Fluorescence images in DCM (CH₂Cl₂) under UV light (λex = 365 nm) and in the solid state, respectively.

To gain preliminary insight into the mechanism of the oxidative Heck reaction, we carried out some deuterium-labeling experiments (Scheme 5). The hydrogen/deuterium exchange experiment indicated that the C2 position of C–H bond cleavage was a reversible process (Scheme 5a). The parallel competition reactions between 1a and 1a-d with styrene 2a resulted in a primary kinetic isotopic effect (k_H/k_D = 1.72) (Scheme 5b), exhibiting that the C–H bond cleavage might be related to the rate-determining step.¹⁸

Based on the above experiments and reported Pd(II)-catalyzed C–H bond oxidative Heck reaction,¹⁹ a plausible mechanism was proposed (Scheme 6). First, reversible C–H activation of benzo[b]thiophene 1,1-dioxide 1a with Pd(II) afforded the intermediate IM1. Next, IM1 coordinated with styrene 2a to form IM2, which was transformed to intermediate IM3 via a migratory insertion process. IM3 underwent β-hydride elimination to release the desired product 3a and Pd(II)H species. Finally, a reductive elimination of Pd(II)H species resulted in Pd(0) species, which then was reoxidized to active Pd(II) catalyst by AgOPiv to complete the catalytic cycle.

Conclusions

In conclusion, we have disclosed the first Pd(II)-catalyzed C2-selective oxidative alkenylation of benzo[b]thiophene 1,1-dioxides and with alkenes via direct C–H bond activation strategy. This oxidative cross-coupling tolerates various benzo[b]thiophene 1,1-dioxides and benzodithiophene S,S-tetraoxides substrates with broad functional group tolerance. In addition, the photophysical properties of several alkenylated products were investigated, which indicate the potential usefulness of our protocol in constructing thiophene 1,1-dioxide-alkene-type π-conjugated skeletons.

Experimental Section

General

NMR spectra were obtained on Bruker AV-400 MHz and AV-600 MHz spectrometers. The ¹H NMR chemical shifts were measured relative to CDCl₃ or DMSO-d₆ as the internal reference (CDCl₃: δ = 7.26 ppm; DMSO-d₆: δ = 2.50 ppm). The ¹³C NMR chemical shifts were given using CDCl₃ as the internal standard (CDCl₃: δ = 77.16 ppm; DMSO-d₆: δ = 39.52 ppm). High-resolution mass spectra (HRMS) were obtained with a Waters-Q-TOF-Premier (ESI). Unless otherwise noted, all reagents were obtained from commercial suppliers and used without further purification.

Unless otherwise noted, all reagents were obtained from commercial suppliers and used without further purification. PivOD (>95% deuterium incorporation by 1H NMR analysis)²⁰ and 2-deuterated benzo[b]thiophene (>95% deuterium incorporation by ¹H NMR analysis)²¹ were prepared according to the literature procedures. Ultradry solvents including N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), isopropanol (IPA), 1,2-dichloroethane (DCE), and 1,4-dioxane were purchased from J&K Scientific. Tetrahydrofuran (THF) and methyl tert-butyl ether (MTBE) were dried by refluxing over Na and freshly distilled prior to use.

General Procedure for the Preparation of Benzo[b]thiophene 1,1-Dioxides²²

H₂O₂ (30%, 6.5 equiv) was slowly added to the solution of benzo[b]thiophene (10 mmol) in 11 mL of AcOH. The mixture was stirred at 100 °C for 1.5 h. After cooling to room temperature, the reaction mixture was treated with saturated aqueous NaHCO₃ solution, and the pH was adjusted to 7. The resulting mixture was extracted with DCM (20 mL × 3), washed with brine, and dried over anhydrous Na₂SO₄. The solvent was removed under reduced pressure, and the residue was purified by flash column chromatography on silica gel to give the corresponding product.

3-Methylbenzo[b]thiophene 1,1-Dioxide (1b)

The product was isolated by flash chromatography (petroleum ether/EtOAc = 5:1, v/v) as a white solid. 68% yield. Mp: 115–116 °C. ¹H NMR (400 MHz, CDCl₃): δ = 7.73–7.70 (m, 1H), 7.62–7.52 (m, 2H), 7.41 (d, J = 7.6 Hz, 1H), 6.47 (q, J = 1.6 Hz, 1H), 2.28 (d, J = 1.6 Hz, 3H) ppm. ¹³C NMR (101 MHz, CDCl₃): δ 143.0, 137.7, 133.6, 133.3, 130.6, 125.9, 122.4, 121.1, 14.0 ppm. IR (cm^–1): 3082, 2921, 2851, 1593, 1440, 1286, 1177, 1106, 832, 765, 606. HRMS (ESI): calcd for C₉H₉O₂S [M + H]⁺ 181.0323, found 181.0313.

5-Methylbenzo[b]thiophene 1,1-Dioxide (1c)

The product was isolated by flash chromatography (petroleum ether/EtOAc = 5:1, v/v) as a white solid. 74% yield. Mp: 118–119 °C. ¹H NMR (400 MHz, CDCl₃): δ = 7.60 (d, J = 7.6 Hz, 1H), 7.32 (d, J = 7.6 Hz, 1H), 7.17–7.16 (m, 2H), 6.69 (d, J = 7.2 Hz, 1H), 2.43 (s, 3H) ppm. ¹³C NMR (101 MHz, CDCl₃): δ 144.8, 134.1, 132.5, 131.7, 131.3, 131.1, 126.2, 121.4, 21.8 ppm. IR (cm^–1): 3092, 1557, 1288, 1168, 1134, 852, 820, 763, 696, 622. HRMS (ESI): calcd for C₉H₉O₂S [M + H]⁺ 181.0323, found 181.0317.

6-Methylbenzo[b]thiophene 1,1-Dioxide (1d)

The product was isolated by flash chromatography (petroleum ether/EtOAc = 5:1, v/v) as a white solid. 70% yield. Mp: 123–125 °C. ¹H NMR (400 MHz, CDCl₃): δ = 7.52 (s, 1H), 7.34 (d, J = 7.6 Hz, 1H), 7.23 (d, J = 8.0 Hz, 1H), 7.18 (d, J = 7.2 Hz, 1H), 6.65 (d, J = 6.8 Hz, 1H), 2.44 (s, 3H) ppm. ¹³C NMR (101 MHz, CDCl₃): δ 141.9, 137.0, 134.2, 132.5, 129.9, 128.7, 125.2, 122.2, 21.6 ppm. IR (cm^–1): 3078, 2923, 2849, 1543, 1282, 1199, 1144, 1063, 819, 742, 632. HRMS (ESI): calcd for C₉H₉O₂S [M + H]⁺ 181.0323, found 181.0328.

3,5-Dimethylbenzo[b]thiophene 1,1-Dioxide (1e)

The product was isolated by flash chromatography (petroleum ether/EtOAc = 5:1, v/v) as a white solid. 65% yield. Mp: 138–140 °C. ¹H NMR (400 MHz, CDCl₃): δ = 7.54 (d, J = 8.0 Hz, 1H), 7.29 (d, J = 8.0 Hz, 1H), 7.18 (s, 1H), 6.41 (d, J = 2.0 Hz, 1H), 2.42 (s, 3H), 2.21 (d, J = 1.6 Hz, 3H) ppm. ¹³C NMR (101 MHz, CDCl₃): δ 144.5, 143.0, 134.8, 133.4, 130.7, 126.1, 123.1, 120.7, 21.8, 13.8 ppm. IR (cm^–1): 3082, 2920, 2851, 1578, 1285, 1177, 1107, 832, 765, 606. HRMS (ESI): calcd for C₁₀H₁₁O₂S [M + H]⁺ 195.0480, found 195.0488.

5-(tert-Butyl)benzo[b]thiophene 1,1-Dioxide (1f)

The product was isolated by flash chromatography (petroleum ether/EtOAc = 6:1, v/v) as a white solid. 60% yield. Mp: 76–77 °C. ¹H NMR (400 MHz, CDCl₃): δ = 7.64 (d, J = 8.0 Hz, 1H), 7.53 (d, J = 7.6 Hz, 1H), 7.36 (s, 1H), 7.20 (d, J = 7.2 Hz, 1H), 6.69 (d, J = 6.8 Hz, 1H), 1.34 (s, 9H) ppm. ¹³C NMR (101 MHz, CDCl₃): δ 158.1, 134.1, 132.8, 131.6, 131.0, 127.8, 122.9, 121.3, 35.5, 31.2 ppm. IR (cm^–1): 3086, 2962, 2362, 1552, 1323, 1294, 1190, 1138, 854, 697, 608. HRMS (ESI): calcd for C₁₂H₁₅O₂S [M + H]⁺ 223.0793, found 223.0790.

5-Methoxybenzo[b]thiophene 1,1-Dioxide (1g)

The product was isolated by flash chromatography (petroleum ether/EtOAc = 4:1, v/v) as a white solid. 55% yield. Mp: 125–126 °C. ¹H NMR (400 MHz, CDCl₃): δ = 7.27–7.25 (m, 2H), 7.17 (dd, J = 6.8, 0.8 Hz, 1H), 7.02 (dd, J = 8.4, 2.4 Hz, 1H), 6.61 (d, J = 6.8 Hz, 1H), 3.88 (s, 3H) ppm. ¹³C NMR (101 MHz, CDCl₃): δ 162.2, 138.6, 132.6, 129.0, 126.4, 123.4, 118.9, 107.7, 56.2 ppm. IR (cm^–1): 3077, 2960, 2360, 1589, 1280, 1251, 1183, 1146, 771, 760, 635. HRMS (ESI): calcd for C₉H₉O₃S [M + H]⁺ 197.0272, found 197.0260.

5-Phenylbenzo[b]thiophene 1,1-Dioxide (1h)

The product was isolated by flash chromatography (petroleum ether/EtOAc = 6:1, v/v) as a white solid. 80% yield. Mp: 148–150 °C. ¹H NMR (400 MHz, CDCl₃): δ = 7.77 (d, J = 7.6 Hz, 1H), 7.71 (d, J = 8.0 Hz, 1H), 7.58–7.55 (m, 3H), 7.51–7.44 (m, 3H), 7.27 (d, J = 6.8 Hz, 1H), 6.76 (d, J = 6.8 Hz, 1H) ppm. ¹³C NMR (101 MHz, CDCl₃): δ 147.3, 139.1, 135.3, 132.4, 132.2, 131.4, 129.5, 129.3, 128.9, 127.4, 124.3, 121.9 ppm. IR (cm^–1): 3067, 2961, 2361, 1603, 1280, 1163, 1101, 782, 768, 743, 630. HRMS (ESI): calcd for C₁₄H₁₁O₂S [M + H]⁺ 243.0480, found 243.0471.

Preparation of 4,8-Bis((2-ethylhexyl)oxy)benzo[1,2-b:4,5-b′]dithiophene 1,1,5,5-Tetraoxide (1i)

H₂O₂ (30%, 13 equiv) was slowly added to the solution of 4,8-bis((2-ethylhexyl)oxy)benzo[1,2-b:4,5-b′]dithiophene (5 mmol) in 6 mL of AcOH. The mixture was stirred at 100 °C for 1.5 h. After cooling to room temperature, the reaction mixture was treated with saturated aqueous NaHCO₃ solution, and the pH was adjusted to 7. The resulting mixture was extracted with DCM (20 mL × 3), washed with brine, and dried over anhydrous Na₂SO₄. Solvent was removed under reduced pressure, and the residue was purified by flash column chromatography (petroleum ether/EtOAc = 2:1, v/v) on silica gel to give the corresponding product 1i (54%). Mp: 153–155 °C. ¹H NMR (400 MHz, CDCl₃): δ = 7.38 (d, J = 6.8 Hz, 2H), 6.70 (d, J = 7.8 Hz, 2H), 4.36 (d, J = 5.6 Hz, 4H), 1.82–1.76 (m, 2H), 1.57–1.31 (m, 16H), 0.98–0.89 (m, 12H) ppm. ¹³C NMR (101 MHz, CDCl₃): δ 145.2, 131.3, 130.8, 128.3, 127.2, 79.0, 40.4, 30.3, 29.1, 23.8, 23.1, 14.2, 11.3 ppm. IR (cm^–1): 3096, 2958, 2928, 2859, 1577, 1446, 1310, 1135, 999, 837, 748, 637. HRMS (ESI): calcd for C₂₆H₃₉O₆S₂ [M + H]⁺ 511.2188, found 511.2168.

General Procedure for the C–H Olefination of Thiophene 1,1-Dioxides

In a nitrogen-filled glovebox, thiophene 1,1-dioxide derivative 1 (0.2 mmol, 1.0 equiv), alkene 2 (0.3 mmol, 1.5 equiv), Pd(OAc)₂ (2.2 mg, 5 mol %), AgOPiv (125 mg, 0.6 mmol, 3.0 equiv), PivOH (61 mg, 0.6 mmol, 3.0 equiv), and THF (1.2 mL) were added to a 10 mL Schlenk tube. The reaction mixture was stirred at 80 °C for 12 h. The solution was filtered through a celite pad and washed with 10 mL of dichloromethane. The filtrate was concentrated, and the residue was purified by column chromatography on silica gel to provide the desired product.

(E)-2-Styrylbenzo[b]thiophene 1,1-Dioxide (3a)

The product was isolated by flash chromatography (petroleum ether/EtOAc = 5:1, v/v) as a green solid. 92% yield. Mp: 172–174 °C. ¹H NMR (600 MHz, CDCl₃): δ = 7.74 (d, J = 7.8 Hz, 1H), 7.55–7.53 (m, 3H), 7.47 (t, J = 7.2 Hz, 1H), 7.41–7.32 (m, 5H), 6.94 (s, 1H), 6.89 (t, J = 16.8 Hz, 1H) ppm. ¹³C NMR (101 MHz, CDCl₃): δ 141.8, 137.5, 136.3, 135.9, 133.9, 132.0, 129.8, 129.4, 129.0, 127.4, 125.1, 124.9, 121.5, 114.9 ppm. IR (cm^–1): 3024, 2921, 2360, 1559, 1445, 1300, 1145, 1118, 962, 888, 752, 690. HRMS (ESI): calcd for C₁₆H₁₃O₂S [M + H]⁺ 269.0636, found 269.0623.

(E)-2-(4-Methylstyryl)benzo[b]thiophene 1,1-Dioxide (3b)

The product was isolated by flash chromatography (petroleum ether/EtOAc = 5:1, v/v) as a green solid. 78% yield. Mp: 187–189 °C. ¹H NMR (400 MHz, CDCl₃): δ = 7.74 (d, J = 7.6 Hz, 1H), 7.54 (td, J = 7.6, 1.2 Hz, 1H), 7.48–7.33 (m, 5H), 7.18 (d, J = 8.0 Hz, 2H), 6.90 (s, 1H), 6.85 (d, J = 16.4 Hz, 1H), 2.37 (s, 3H) ppm. ¹³C NMR (101 MHz, CDCl₃): δ 142.1, 139.7, 137.5, 136.4, 133.9, 133.2, 132.1, 129.7, 129.7, 127.4, 124.9, 124.2, 121.6, 113.9, 21.6 ppm. IR (cm^–1): 3025, 2920, 2360, 1584, 1458, 1301, 1149, 1117, 963, 889, 758, 591. HRMS (ESI): calcd for C₁₇H₁₄NaO₂S [M + Na]⁺ 305.0612, found 305.0606.

(E)-2-(3-Methylstyryl)benzo[b]thiophene 1,1-Dioxide (3c)

The product was isolated by flash chromatography (petroleum ether/EtOAc = 5:1, v/v) as a green solid. 71% yield. Mp: 133–135 °C. ¹H NMR (600 MHz, CDCl₃): δ = 7.74 (d, J = 7.2 Hz, 1H), 7.68 (d, J = 16.2 Hz, 1H), 7.56–7.52 (m, 2H), 7.46 (t, J = 7.2 Hz, 1H), 7.35 (d, J = 7.2 Hz, 1H), 7.24–7.19 (m, 3H), 6.93 (s, 1H), 6.80 (d, J = 16.2 Hz, 1H), 2.47 (s, 3H) ppm. ¹³C NMR (151 MHz, CDCl₃): δ 142.1, 137.5, 137.3, 134.9, 134.2, 133.9, 132.0, 130.1, 129.8, 129.3, 126.4, 125.3, 125.0, 124.7, 121.5, 115.8, 19.9 ppm. IR (cm^–1): 3057, 2924, 2361, 1589, 1459, 1295, 1147, 1056, 956, 889, 751, 732, 592. HRMS (ESI): calcd for C₁₇H₁₄NaO₂S [M + Na]⁺ 305.0612, found 305.0602.

(E)-2-(2-Methylstyryl)benzo[b]thiophene 1,1-Dioxide (3d)

The product was isolated by flash chromatography (petroleum ether/EtOAc = 5:1, v/v) as a green solid. 44% yield. Mp: 150–151 °C. ¹H NMR (400 MHz, CDCl₃): δ = 7.75 (d, J = 7.6 Hz, 1H), 7.68 (d, J = 16.4 Hz, 1H), 7.57–7.53 (m, 2H), 7.47 (td, J = 7.6, 1.2 Hz, 1H), 7.36 (d, J = 7.6 Hz, 1H), 7.25–7.19 (m, 3H), 6.94 (s, 1H), 6.80 (d, J = 16.4 Hz, 1H), 2.47 (s, 3H) ppm. ¹³C NMR (101 MHz, CDCl₃): δ 142.2, 137.6, 137.3, 135.0, 134.3, 133.9, 132.0, 130.9, 129.8, 129.3, 126.4, 125.4, 125.0, 124.6, 121.6, 115.8, 19.9 ppm. IR (cm^–1): 3056, 2924, 2360, 1588, 1459, 1296, 1146, 1116, 955, 886, 749, 731, 591. HRMS (ESI): calcd for C₁₇H₁₅O₂S [M + H]⁺ 283.0793, found 283.0780.

(E)-2-(4-(tert-Butyl)styryl)benzo[b]thiophene 1,1-Dioxide (3e)

The product was isolated by flash chromatography (petroleum ether/EtOAc = 6:1, v/v) as a green solid. 94% yield. Mp: 182–185 °C. ¹H NMR (400 MHz, DMSO-d₆): δ = 7.89 (d, J = 7.6 Hz, 1H), 7.70 (t, J = 7.6 Hz, 1H), 7.64 (d, J = 7.6 Hz, 1H), 7.60–7.56 (m, 3H), 7.46–7.44 (m, 3H), 7.20 (s, 2H), 1.30 (s, 9H) ppm. ¹³C NMR (101 MHz, DMSO-d₆): δ 152.2, 140.8, 136.7, 134.4, 134.1, 132.9, 131.4, 130.2, 127.0, 125.9, 125.8, 125.8, 121.3, 115.1, 34.6, 31.0 ppm. IR (cm^–1): 2960, 2869, 2336, 1586, 1460, 1303, 1149, 1115, 958, 846, 756, 742, 594. HRMS (ESI): calcd for C₂₀H₂₁O₂S [M + H]⁺ 325.1262, found 325.1249.

(E)-2-(4-Methoxystyryl)benzo[b]thiophene 1,1-Dioxide (3f)

The product was isolated by flash chromatography (petroleum ether/EtOAc = 4:1, v/v) as a green solid. 90% yield. Mp: 196–199 °C. ¹H NMR (400 MHz, DMSO-d₆): δ = 7.88 (d, J = 7.2 Hz, 1H), 7.69 (t, J = 7.6 Hz, 1H), 7.63–7.54 (m, 4H), 7.38 (s, 1H), 7.18 (d, J = 16.8 Hz, 1H), 7.10 (d, J = 16.8 Hz, 1H), 6.99 (d, J = 8.4 Hz, 2H), 3.80 (s, 3H) ppm. ¹³C NMR (101 MHz, DMSO-d₆): δ 160.3, 141.0, 136.6, 134.3, 134.1, 131.6, 129.9, 128.7, 128.2, 125.6, 124.8, 121.2, 114.5, 113.5, 55.3 ppm. IR (cm^–1): 3055, 2361, 2341, 1588, 1507, 1458, 1293, 1142, 1056, 958, 746, 728, 631. HRMS (ESI): calcd for C₁₇H₁₅O₃S [M + H]⁺ 299.0742, found 299.0726.

(E)-2-(3,4-Dimethoxystyryl)benzo[b]thiophene 1,1-Dioxide (3g)

The product was isolated by flash chromatography (petroleum ether/EtOAc = 3:1, v/v) as a green solid. 77% yield. Mp: 227–229 °C. ¹H NMR (400 MHz, CDCl₃): δ = 7.73 (d, J = 7.2 Hz, 1H), 7.52 (td, J = 7.6, 0.8 Hz, 1H), 7.44 (td, J = 7.6, 1.2 Hz, 1H), 7.37–7.30 (m, 2H), 7.12 (dd, J = 8.4, 2.0 Hz, 1H), 7.03 (d, J = 2.0 Hz, 1H), 6.87–6.85 (m, 2H), 6.76 (d, J =16.4 Hz, 1H), 3.93 (s, 3H), 3.91 (s, 3H) ppm. ¹³C NMR (101 MHz, CDCl₃): δ 150.4, 149.3, 142.0, 137.3, 136.1, 133.9, 132.2, 129.5, 129.0, 124.9, 123.6, 121.5, 121.1, 112.9, 111.3, 109.6, 56.1, 56.0 ppm. IR (cm^–1): 3054, 2926, 2360, 1588, 1460, 1298, 1149, 1056, 960, 752, 734, 635. HRMS (ESI): calcd for C₁₈H₁₇O₄S [M + H]⁺ 329.0848, found 329.0859.

(E)-4-(2-(1,1-Dioxidobenzo[b]thiophen-2-yl)vinyl)phenyl Acetate (3h)

The product was isolated by flash chromatography (petroleum ether/EtOAc = 3:1, v/v) as a yellow solid. 63% yield. Mp: 183–184 °C. ¹H NMR (400 MHz, CDCl₃): δ = 7.74 (d, J = 7.6 Hz, 1H), 7.56–7.52 (m, 3H), 7.46 (td, J = 7.6, 1.2 Hz, 1H), 7.39 (d, J = 16.4 Hz, 1H), 7.34 (d, J = 7.6 Hz, 1H), 7.13–7.10 (m, 2H), 6.94 (d, J = 0.8 Hz, 1H), 6.83 (dd, J = 16.4, 0.8 Hz, 1H), 2.31 (s, 3H) ppm. ¹³C NMR (101 MHz, CDCl₃): δ 169.4, 151.5, 141.7, 137.5, 135.1, 133.9, 133.7, 131.9, 129.9, 128.4, 125.1, 122.2, 121.6, 115.1, 21.3 ppm. IR (cm^–1): 3064, 2360, 1756, 1580, 1504, 1372, 1295, 1188, 1163, 909, 849, 760. HRMS (ESI): calcd for C₁₈H₁₅O₄S [M + H]⁺ 327.0691, found 327.0671.

(E)-2-(4-Fluorostyryl)benzo[b]thiophene 1,1-Dioxide (3i)

The product was isolated by flash chromatography (petroleum ether/EtOAc = 6/1, v/v) as a green solid. 60% yield. Mp: 162–164 °C. ¹H NMR (600 MHz, CDCl₃): δ = 7.73 (d, J = 7.2 Hz, 1H), 7.54–7.45 (m, 4H), 7.36 (d, J = 16.8 Hz, 1H), 7.32 (d, J = 7.2 Hz, 1H), 7.05 (t, J = 8.4 Hz, 2H), 6.92 (s, 1H), 6.79 (d, J = 16.2 Hz, 1H) ppm. ¹³C NMR (151 MHz, CDCl₃): δ 164.2, 162.6, 141.6, 137.4, 134.9, 133.9, 132.2, 132.1, 131.9, 129.9, 129.10, 129.05, 125.1, 125.0, 121.6, 116.1, 116.0, 114.7, 114.7 ppm. ¹⁹F NMR (377 MHz, CDCl₃): δ = −111.1 ppm. IR (cm^–1): 3057, 2924, 2361, 1588, 1490, 1295, 1144, 1138, 1086, 957, 810, 752. HRMS (ESI): calcd for C₁₆H₁₂FO₂S [M + H]⁺ 287.0542, found 287.0531.

(E)-2-(4-Chlorostyryl)benzo[b]thiophene 1,1-Dioxide (3j)

The product was isolated by flash chromatography (petroleum ether/EtOAc = 6:1, v/v) as a green solid. 63% yield. Mp: 174–175 °C. ¹H NMR (400 MHz, CDCl₃): δ = 7.75 (d, J = 7.2 Hz, 1H), 7.55 (td, J = 7.6, 1.2 Hz, 1H), 7.50–7.45 (m, 3H), 7.38–7.33 (m, 4H), 6.95 (s, 1H), 6.86 (d, J = 16.4 Hz, 1H) ppm. ¹³C NMR (101 MHz, CDCl₃): δ 141.6, 137.5, 135.2, 134.8, 134.4, 134.0, 131.9, 130.0, 129.2, 128.5, 125.4, 125.2, 121.6, 115.5 ppm. IR (cm^–1): 3058, 2923, 2360, 1586, 1489, 1458, 1297, 1147, 1090, 1056, 956, 843, 808, 753. HRMS (ESI): calcd for C₁₆H₁₂ClO₂S [M + H]⁺ 303.0247, found 303.0243.

(E)-2-(4-(Trifluoromethyl)styryl)benzo[b]thiophene 1,1-Dioxide (3k)

The product was isolated by flash chromatography (petroleum ether/EtOAc = 6:1, v/v) as a green solid. 50% yield. Mp: 185–187 °C. ¹H NMR (600 MHz, CDCl₃): δ = 7.76 (d, J = 7.2 Hz, 1H), 7.63–7.62 (m, 4H), 7.57 (t, J = 7.2 Hz, 1H), 7.51 (t, J = 7.2 Hz, 1H), 7.42 (d, J = 16.2 Hz, 1H), 7.38 (d, J = 7.2 Hz, 1H), 7.02 (s, 1H), 6.96 (d, J = 16.8 Hz, 1H) ppm. ¹³C NMR (151 MHz, CDCl₃): δ 141.3, 139.3, 137.6, 134.4, 134.0, 131.7, 130.3, 127.5, 126.5, 126.0, 125.92, 125.90, 125.4, 121.7, 117.3 ppm. ¹⁹F NMR (377 MHz, CDCl₃): δ = −62.7 ppm. IR (cm^–1): 3058, 2358, 1610, 1416, 1322, 1294, 1148, 1107, 956,872, 753, 738. HRMS (ESI): calcd for C₁₇H₁₁F₃NaO₂S [M + Na]⁺ 359.0330, found 359.0303.

Methyl (E)-4-(2-(1,1-dioxidobenzo[b]thiophen-2-yl)vinyl)benzoate (3l)

The product was isolated by flash chromatography (petroleum ether/EtOAc = 2:1, v/v) as a green solid. 67% yield. Mp: 204–207 °C. ¹H NMR (400 MHz, CDCl₃): δ = 8.03 (d, J = 8.4 Hz, 2H), 7.75 (d, J = 7.6 Hz, 1H), 7.59–7.47 (m, 4H), 7.42 (d, J = 16.8 Hz, 1H), 7.36 (dd, J = 7.2, 1.2 Hz, 1H), 7.00 (s, 1H), 6.97 (d, J = 16.4 Hz, 1H), 3.93 (s, 3H) ppm. ¹³C NMR (101 MHz, CDCl₃): δ 166.7, 141.4, 140.2, 137.6, 134.9, 134.0, 131.7, 130.5, 130.2, 127.2, 126.3, 125.3, 121.7, 117.2, 52.4 ppm. IR (cm^–1): 3056, 2361, 1757, 1585, 1447, 1290, 1126, 962, 815, 787, 645. HRMS (ESI): calcd for C₁₈H₁₅O₄S [M + H]⁺ 327.0691, found 327.0669.

(E)-2-(2-(Naphthalen-2-yl)vinyl)benzo[b]thiophene 1,1-Dioxide (3m)

The product was isolated by flash chromatography (petroleum ether/EtOAc = 5:1, v/v) as a yellow solid. 61% yield. Mp: 210–212 °C. ¹H NMR (400 MHz, CDCl₃): δ = 7.95 (s, 1H), 7.86–7.80 (m, 3H), 7.76 (d, J = 8.0 Hz, 1H), 7.69 (dd, J = 8.4, 1.6 Hz, 1H), 7.59 (d, J = 16.0 Hz, 1H), 7.54 (dd, J = 7.6, 1.2 Hz, 1H), 7.50–7.45 (m, 3H), 7.36 (d, J = 7.2 Hz, 1H), 7.03–6.97 (m, 2H) ppm. ¹³C NMR (101 MHz, CDCl₃): δ 142.0, 137.5, 136.4, 133.93, 133.90, 133.6, 133.4, 132.1, 129.8, 129.0, 128.7, 128.6, 127.9, 127.0, 126.8, 125.1, 124.8, 123.1, 121.6, 115.1 ppm. IR (cm^–1): 3056, 2923, 2360, 1590, 1462, 1295, 1146, 958, 790, 752, 736. HRMS (ESI): calcd for C₂₀H₁₅O₂S [M + H]⁺ 319.0793, found 319.0781.

Ethyl (E)-3-(1,1-dioxidobenzo[b]thiophen-2-yl)acrylate (3n)

The product was isolated by flash chromatography (petroleum ether/EtOAc = 2:1, v/v) as a green oil. 67% yield. ¹H NMR (600 MHz, CDCl₃): δ = 7.77 (d, J = 7.2 Hz, 1H), 7.62–7.56 (m, 2H), 7.45–7.41 (m, 2H), 7.22 (s, 1H), 6.71 (d, J = 16.2 Hz, 1H), 4.28 (q, J = 7.2 Hz, 2H), 1.33 (t, J = 7.2 Hz, 3H) ppm. ¹³C NMR (101 MHz, CDCl₃): δ 165.8, 139.6, 138.0, 134.1, 131.7, 131.4, 130.8, 129.2, 126.2, 124.9, 121.8, 61.3, 14.3 ppm. IR (cm^–1): 3062, 2360, 1747, 1590, 1445, 1272, 1108, 943, 832, 777. HRMS (ESI): calcd for C₁₃H₁₃O₄S [M + H]⁺ 265.0535, found 265.0530.

tert-Butyl (E)-3-(1,1-dioxidobenzo[b]thiophen-2-yl)acrylate (3o)

The product was isolated by flash chromatography (petroleum ether/EtOAc = 2:1, v/v) as a green oil. 65% yield. ¹H NMR (400 MHz, CDCl₃): δ = 7.75 (d, J = 7.2 Hz, 1H), 7.61-7.53 (m, 2H), 7.43 (d, J = 8.0 Hz, 1H), 7.32 (d, J = 16.4 Hz, 1H), 7.19 (s, 1H), 6.64 (d, J = 16.4 Hz, 1H), 1.51 (s, 9H) ppm. ¹³C NMR (101 MHz, CDCl₃): δ 165.0, 139.8, 137.9, 134.1, 131.3, 131.2, 130.9, 128.2, 126.9, 126.1, 121.8, 81.6, 28.2 ppm. IR (cm^–1): 3060, 2361, 1752, 1592, 1448, 1297, 1122, 959, 847, 760, 624. HRMS (ESI): calcd for C₁₅H₁₇O₄S [M + H]⁺ 293.0848, found 293.0844.

(E)-3-Methyl-2-styrylbenzo[b]thiophene 1,1-Dioxide (4a)

The product was isolated by flash chromatography (petroleum ether/EtOAc = 5:1, v/v) as a green solid. 94% yield. Mp: 198–200 °C. ¹H NMR (400 MHz, CDCl₃): δ = 7.77 (d, J = 7.6 Hz, 1H), 7.62–7.55 (m, 3H), 7.52–7.43 (m, 3H), 7.40–7.32 (m, 3H), 6.95 (d, J = 16.4 Hz, 1H), 2.33 (s, 3H) ppm. ¹³C NMR (101 MHz, CDCl₃): δ 136.7, 136.4, 135.9, 135.1, 133.9, 133.8, 133.5, 129.8, 129.2, 128.9, 127.2, 122.3, 121.1, 113.4, 11.48. IR (cm^–1): 3057, 2359, 1587, 1461, 1291, 1150, 1118, 950, 760, 686. HRMS (ESI): calcd for C₁₇H₁₅O₂S [M + H]⁺ 283.0793, found 283.0785.

(E)-5-Methyl-2-styrylbenzo[b]thiophene 1,1-Dioxide (4b)

The product was isolated by flash chromatography (petroleum ether/EtOAc = 5:1, v/v) as a green solid. 73% yield. Mp: 199–201 °C. ¹H NMR (400 MHz, CDCl₃): δ = 7.62 (d, J = 7.6 Hz, 1H), 7.53–7.50 (m, 2H), 7.43–7.30 (m, 4H), 7.25 (d, J = 8.0 Hz, 1H), 7.14 (s, 1H), 6.89-6.85 (m, 2H), 2.41 (s, 3H) ppm. ¹³C NMR (101 MHz, CDCl₃): δ 144.9, 142.1, 136.1, 136.0, 134.8, 132.3, 130.3, 129.4, 128.9, 127.3, 125.8, 125.0, 121.4, 115.0, 21.9 ppm. IR (cm^–1): 3041, 2361, 1583, 1444, 1284, 1145, 1118, 944, 762, 743, 616. HRMS (ESI): calcd for C₁₇H₁₅O₂S [M + H]⁺ 283.0793, found 283.0774.

(E)-4-Methyl-2-styrylbenzo[b]thiophene 1,1-Dioxide (4c)

The product was isolated by flash chromatography (petroleum ether/EtOAc = 5:1, v/v) as a green solid. 88% yield. Mp: 202–203 °C. ¹H NMR (400 MHz, CDCl₃): δ = 7.77 (d, J = 7.6 Hz, 1H), 7.62–7.55 (m, 3H), 7.52–7.44 (m, 3H), 7.40–7.32 (m, 2H), 7.34–7.30 (m, 1H), 6.95 (d, J = 16.4 Hz, 1H), 2.33 (s, 3H) ppm. ¹³C NMR (101 MHz, CDCl₃): δ 136.8, 136.4, 136.0, 135.1, 133.9, 133.8, 133.5, 129.8, 129.2, 128.9, 127.3, 122.3, 121.1, 113.5 ppm. IR (cm^–1): 3057, 2921, 1581, 1448, 1300, 1140, 955, 752, 690. HRMS (ESI): calcd for C₁₇H₁₅O₂S [M + H]⁺ 283.0793, found 283.0782.

(E)-3,5-Dimethyl-2-styrylbenzo[b]thiophene 1,1-Dioxide (4d)

The product was isolated by flash chromatography (petroleum ether/EtOAc = 5:1, v/v) as a green solid. 69% yield. M.p.: 206-208 °C. ¹H NMR (400 MHz, CDCl₃): δ = 7.64 (d, J = 8.0 Hz, 1H), 7.56–7.54 (m, 2H), 7.46–7.28 (m, 5H), 7.22 (s, 1H), 6.94 (d, J = 16.4 Hz, 1H), 2.45 (s, 3H), 2.30 (s, 3H) ppm. ¹³C NMR (101 MHz, CDCl₃): δ 144.7, 136.4, 136.1, 134.8, 134.1, 134.0, 133.7, 130.3, 129.1, 128.9, 127.2, 123.0, 121.0, 113.5, 22.1, 11.4. IR (cm^–1): 3056, 2920, 2360, 1591, 1447, 1281, 1146, 1126, 949, 813, 746. HRMS (ESI): calcd for C₁₈H₁₇O₂S [M + H]⁺ 297.0949, found 297.0930.

(E)-5-(tert-Butyl)-2-styrylbenzo[b]thiophene 1,1-Dioxide (4e)

The product was isolated by flash chromatography (petroleum ether/EtOAc = 6:1, v/v) as a green solid. 82% yield. Mp: 205–207 °C. ¹H NMR (400 MHz, CDCl₃): δ = 7.67 (d, J = 8.0 Hz, 1H), 7.54 (d, J = 7.2 Hz, 2H), 7.48 (d, J = 8.0 Hz, 1H), 7.43-7.32 (m, 5H), 6.93-6.87 (m, 2H), 1.35 (s, 9H) ppm. ¹³C NMR (101 MHz, CDCl₃): δ 158.2, 142.0, 136.01, 135.97, 134.7, 132.1, 129.3, 128.9, 127.4, 126.9, 125.4, 122.4, 121.3, 115.0, 35.5, 31.2 ppm. IR (cm^–1): 2961, 2869, 2360, 1587, 1460, 1300, 1149, 1116, 959, 846, 756, 742. HRMS (ESI): calcd for C₂₀H₂₁O₂S [M + H]⁺ 325.1262, found 325.1256.

(E)-5-Methoxy-2-styrylbenzo[b]thiophene 1,1-Dioxide (4f)

The product was isolated by flash chromatography (petroleum ether/EtOAc = 4:1, v/v) as a green solid. 61% yield. Mp: 197–199 °C. ¹H NMR (400 MHz, CDCl₃): δ = 7.52 (d, J = 5.6 Hz, 2H), 7.38–7.27 (m, 6H), 7.04 (dd, J = 5.6 Hz, 1.6 Hz, 1H), 6.90–6.85 (m, 2H), 3.89 (s, 3H) ppm. ¹³C NMR (101 MHz, CDCl₃): δ 161.5, 140.5, 139.2, 136.1, 134.8, 129.2, 128.9, 127.2, 126.1, 125.1, 124.2, 119.6, 115.1, 107.4, 56.2. IR (cm^–1): 2360, 2342, 1489, 1295, 1231, 1144, 1045, 962, 879, 753, 699. HRMS (ESI): calcd for C₁₇H₁₅O₃S [M + H]⁺ 299.0742, found 299.0732.

(E)-5-Phenyl-2-styrylbenzo[b]thiophene 1,1-Dioxide (4g)

The product was isolated by flash chromatography (petroleum ether/EtOAc = 6:1, v/v) as a green solid. 73% yield. Mp: 218–221 °C. ¹H NMR (400 MHz, CDCl₃): δ = 7.81 (d, J = 8.0 Hz, 1H), 7.66 (dd, J = 7.6 Hz, 1.6 Hz, 1H), 7.60–7.35 (m, 12H), 6.99-6.90 (m, 2H) ppm. ¹³C NMR (101 MHz, CDCl₃): δ 147.4, 142.5, 139.3, 136.5, 136.0, 135.9, 132.8, 129.5, 129.3, 129.0, 128.9, 128.5, 127.43, 127.41, 124.8, 123.8, 121.9, 114.9. IR (cm^–1): 3057, 2923, 2360, 1591, 1462, 1296, 1150, 960, 887, 763, 742. HRMS (ESI): calcd for C₂₂H₁₇O₂S [M + H]⁺ 345.0949, found 345.0931

4,8-Bis((2-ethylhexyl)oxy)-2,6-di((E)-styryl)benzo[1,2-b:4,5-b′]dithiophene 1,1,5,5-Tetraoxide (4h)

Styrene 2a (0.6 mmol, 3.0 equiv) was used. The product was isolated by flash chromatography (petroleum ether/EtOAc = 5:1, v/v) as a yellow solid. 78% yield. Mp: 218–220 °C. ¹H NMR (600 MHz, CDCl₃): δ = 7.55 (d, J = 7.2 Hz, 4H), 7.44-7.36 (m, 8H), 7.07 (s, 2H), 6.91 (d, J = 16.2 Hz, 2H), 4.40 (dd, J = 5.4 Hz, 1.2 Hz, 4H), 1.88–1.84 (m, 2H), 1.65–1.59 (m, 2H), 1.58–1.47 (m, 6H), 1.42–1.36 (m, 8H), 1.02 (t, J = 7.2 Hz, 6H), 0.95 (t, J = 7.2 Hz, 6H) ppm. ¹³C NMR (101 MHz, CDCl₃): δ 145.3, 141.8, 137.1, 135.8, 131.8, 129.8, 129.1, 128.1, 127.5, 119.5, 114.9, 79.1, 40.6, 30.4, 29.2, 23.8, 23.2, 14.3, 11.32. IR (cm^–1): 2956, 2928, 2361, 1445, 1376, 1304, 1242, 1138, 1035, 943, 871, 686. HRMS (ESI): calcd for C₄₂H₅₁O₆S₂ [M + H]⁺ 715.3127, found 715.3133.

Acknowledgments

This work was supported by grants from the National NSF of China (no. 22101259) and the Zhejiang Provincial Natural Science Foundation of China (no. LQ22B020002).

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.2c07427.

Experimental procedures; characterization data; X-ray data; and copies of NMR spectra (PDF)

The authors declare no competing financial interest.

Supplementary Material

ao2c07427_si_001.pdf^{(7.6MB, pdf)}

References

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[ref4] Barbarella G.; Favaretto L.; Sotgiu G.; Zambianchi M.; Bongini A.; Arbizzani C.; Mastragostino M.; Anni M.; Gigli G.; Cingolani R. Tuning Solid-State Photoluminescence Frequencies and Efficiencies of Oligomers Containing One Central Thiophene-S,S-dioxide Unit. J. Am. Chem. Soc. 2000, 122, 11971–11978. 10.1021/ja002037p. [DOI] [Google Scholar]

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[ref6] a Guo J.; Hu S.; Luo W.; Hu R.; Qin A.; Zhao Z.; Tang B. Z. A novel aggregation-induced emission platform from 2,3-diphenylbenzo[b]thiophene S,S-dioxide. Chem. Commun. 2017, 53, 1463–1466. 10.1039/C6CC09892D. [DOI] [PubMed] [Google Scholar]; b Zhen S.; Guo J.; Luo W.; Qin A.; Zhao Z.; Tang B. Z. Synthesis, structure, photoluminescence and photochromism of phosphindole oxide and benzo[b]thiophene S,S-dioxide derivatives. J. Photochem. Photobiol., A 2018, 355, 274–282. 10.1016/j.jphotochem.2017.08.061. [DOI] [Google Scholar]

[ref7] For selected examples; a Fukazawa A.; Oshima H.; Shimizu S.; Kobayashi N.; Yamaguchi S. Dearomatization-Induced Transannular Cyclization: Synthesis of Electron-Accepting Thiophene-S,S-Dioxide-Fused Biphenylene. J. Am. Chem. Soc. 2014, 136, 8738–8745. 10.1021/ja503499n. [DOI] [PubMed] [Google Scholar]; b Chen B.; Zhang H.; Luo W.; Nie H.; Hu R.; Qin A.; Zhao Z.; Tang B. Z. Oxidation-Enhanced Emission: Exploring Novel AIEgens from Thieno[3,2-b]thiophene S,S-dioxide. J. Mater. Chem. C 2017, 5, 960–968. 10.1039/C6TC05116B. [DOI] [Google Scholar]; c Di Maria F.; Zanelli A.; Liscio A.; Kovtun A.; Salatelli E.; Mazzaro R.; Morandi V.; Bergamini G.; Shaffer A.; Rozen S. Poly(3-Hexylthiophene) Nanoparticles Containing Thiophene-S,S-Dioxide: Tuning of Dimensions, Optical and Redox Properties, and Charge Separation under Illumination. ACS Nano 2017, 11, 1991–1999. 10.1021/acsnano.6b08176. [DOI] [PubMed] [Google Scholar]; d Zhang Y.; Peng F.; He R.; Ying L.; Yang W.; Cao Y. Synthesis and Properties of Five Ring Fused Aromatic Compounds Based on S, S-Dioxide Benzothiophene. New J. Chem. 2018, 42, 2750–2757. 10.1039/C7NJ04306F. [DOI] [Google Scholar]; e Hu Q.; Jiang H.; Cui Z.; Chen W. An insight into the effect of S,S-dioxided thiophene on the opto-physical/electro-chemical properties and light stability for indophenine derivatives. Dyes Pigm. 2020, 173, 107891 10.1016/j.dyepig.2019.107891. [DOI] [Google Scholar]

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[ref11] a Khambhati D. P.; Sachinthani K. A. N.; Rheingold A. L.; Nelson T. L. Regioselective copper-catalyzed direct arylation of benzodithiophene-S,S-tetraoxide. Chem. Commun. 2017, 53, 5107–5109. 10.1039/C7CC01781B. [DOI] [PubMed] [Google Scholar]; b Ajitha M. J.; Pary F.; Nelson T. L.; Musaev D. G. Unveiling the Role of Base and Additive in the Ullmann-Type of Arene-Aryl C-C Coupling Reaction. ACS Catal. 2018, 8, 4829–4837. 10.1021/acscatal.8b00837. [DOI] [Google Scholar]

[ref12] Punzi A.; Capozzi M. A. M.; Noja S. D.; Ragni R.; Zappimbulso N.; Farinola G. M. Solvent-Free Pd-Catalyzed Heteroaryl-Aryl Coupling via C-H Bond Activation for the Synthesis of Extended Heteroaromatic Conjugated Molecules. J. Org. Chem. 2018, 83, 9312–9321. 10.1021/acs.joc.8b01284. [DOI] [PubMed] [Google Scholar]

[ref13] Kathiravan S.; Nicholls I. A. Cobalt-Catalyzed Oxidative Annulation of Benzothiophene-[b]-1,1-dioxide through Diastereoselective Double C–H Activation. Org. Lett. 2019, 21, 9806–9811. 10.1021/acs.orglett.9b03158. [DOI] [PubMed] [Google Scholar]

[ref14] Kumaran S.; Parthasarathy K. Rh(III)-Catalyzed Oxidative C–2 Coupling of N-Pyridinylindoles with Benzo[b]thiophene 1,1-Dioxides via C–H Bond Activation. J. Org. Chem. 2021, 86, 7987–7999. 10.1021/acs.joc.1c00301. [DOI] [PubMed] [Google Scholar]

[ref15] CCDC 2211923 (3a) contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

[ref16] Maehara A.; Satoh T.; Miura M. Palladium-catalyzed direct oxidative vinylation of thiophenes and furans under weakly basic conditions. Tetrahedron 2008, 64, 5982–5986. 10.1016/j.tet.2008.01.058. [DOI] [Google Scholar]

[ref17] a Chou T.-s.; Chen M.-M. Chemoselective Reactions of Ultrasonically Dispersed Potassium with Some Brominated Hydrothiophene S,S-Dioxides. Heterocycles 1987, 26, 2829–2834. 10.3987/R-1987-11-2829. [DOI] [Google Scholar]; b Nakayama J.; Sugihara Y.. In Organosulfur Chemistry (Synthetic Aspects); Page P., Ed.; Academic Press: NewYork, 1998. [Google Scholar]

[ref18] Simmons E. M.; Hartwig J. F. On the Interpretation of Deuterium Kinetic Isotope Effects in C-H Bond Functionalizations by Transition-Metal Complexes. Angew. Chem., Int. Ed. 2012, 51, 3066–3072. 10.1002/anie.201107334. [DOI] [PubMed] [Google Scholar]

[ref19] a Le Bras J.; Muzart J. Intermolecular Dehydrogenative Heck Reactions. Chem. Rev. 2011, 111, 1170–1214. 10.1021/cr100209d. [DOI] [PubMed] [Google Scholar]; b Huang X.; Huang J.; Du C.; Zhang X.; Song F.; You J. N-Oxide as a traceless oxidizing directing group: mild rhodium(III)-catalyzed C-H olefination for the synthesis of ortho-alkenylated tertiary anilines. Angew. Chem., Int. Ed. 2013, 52, 12970–12974. 10.1002/anie.201307174. [DOI] [PubMed] [Google Scholar]

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Palladium-Catalyzed C2-Selective Oxidative Olefination of Benzo[b]thiophene 1,1-Dioxides with Styrenes and Acrylates

Bingbin Yang

Yaoyao Lu

Luqiong Duan

Xiaoyu Ma

Yaolin Xia

Xiaolei Huang

Abstract

Introduction

Scheme 1. Evolution of Transition-Metal-Catalyzed C–H Activation/Functionalization of Thiophene 1,1-Dioxides.

Results and Discussion

Table 1. Optimization of Pd(II)-Catalyzed Oxidative Heck Reactiona.

Scheme 2. Scope of Alkenes,

Scheme 3. Scope of Benzo[b]thiophene 1,1-Dioxides,,

Scheme 4. Gram-Scale Reaction.

Figure 1.

Scheme 5. Deuterium-Labeling Experiments.

Scheme 6. Plausible Mechanistic Pathway.

Conclusions

Experimental Section

General

General Procedure for the Preparation of Benzo[b]thiophene 1,1-Dioxides22

3-Methylbenzo[b]thiophene 1,1-Dioxide (1b)

5-Methylbenzo[b]thiophene 1,1-Dioxide (1c)

6-Methylbenzo[b]thiophene 1,1-Dioxide (1d)

3,5-Dimethylbenzo[b]thiophene 1,1-Dioxide (1e)

5-(tert-Butyl)benzo[b]thiophene 1,1-Dioxide (1f)

5-Methoxybenzo[b]thiophene 1,1-Dioxide (1g)

5-Phenylbenzo[b]thiophene 1,1-Dioxide (1h)

Preparation of 4,8-Bis((2-ethylhexyl)oxy)benzo[1,2-b:4,5-b′]dithiophene 1,1,5,5-Tetraoxide (1i)

General Procedure for the C–H Olefination of Thiophene 1,1-Dioxides

(E)-2-Styrylbenzo[b]thiophene 1,1-Dioxide (3a)

(E)-2-(4-Methylstyryl)benzo[b]thiophene 1,1-Dioxide (3b)

(E)-2-(3-Methylstyryl)benzo[b]thiophene 1,1-Dioxide (3c)

(E)-2-(2-Methylstyryl)benzo[b]thiophene 1,1-Dioxide (3d)

(E)-2-(4-(tert-Butyl)styryl)benzo[b]thiophene 1,1-Dioxide (3e)

(E)-2-(4-Methoxystyryl)benzo[b]thiophene 1,1-Dioxide (3f)

(E)-2-(3,4-Dimethoxystyryl)benzo[b]thiophene 1,1-Dioxide (3g)

(E)-4-(2-(1,1-Dioxidobenzo[b]thiophen-2-yl)vinyl)phenyl Acetate (3h)

(E)-2-(4-Fluorostyryl)benzo[b]thiophene 1,1-Dioxide (3i)

(E)-2-(4-Chlorostyryl)benzo[b]thiophene 1,1-Dioxide (3j)

(E)-2-(4-(Trifluoromethyl)styryl)benzo[b]thiophene 1,1-Dioxide (3k)

Methyl (E)-4-(2-(1,1-dioxidobenzo[b]thiophen-2-yl)vinyl)benzoate (3l)

(E)-2-(2-(Naphthalen-2-yl)vinyl)benzo[b]thiophene 1,1-Dioxide (3m)

Ethyl (E)-3-(1,1-dioxidobenzo[b]thiophen-2-yl)acrylate (3n)

tert-Butyl (E)-3-(1,1-dioxidobenzo[b]thiophen-2-yl)acrylate (3o)

(E)-3-Methyl-2-styrylbenzo[b]thiophene 1,1-Dioxide (4a)

(E)-5-Methyl-2-styrylbenzo[b]thiophene 1,1-Dioxide (4b)

(E)-4-Methyl-2-styrylbenzo[b]thiophene 1,1-Dioxide (4c)

(E)-3,5-Dimethyl-2-styrylbenzo[b]thiophene 1,1-Dioxide (4d)

(E)-5-(tert-Butyl)-2-styrylbenzo[b]thiophene 1,1-Dioxide (4e)

(E)-5-Methoxy-2-styrylbenzo[b]thiophene 1,1-Dioxide (4f)

(E)-5-Phenyl-2-styrylbenzo[b]thiophene 1,1-Dioxide (4g)

4,8-Bis((2-ethylhexyl)oxy)-2,6-di((E)-styryl)benzo[1,2-b:4,5-b′]dithiophene 1,1,5,5-Tetraoxide (4h)

Acknowledgments

Supporting Information Available

Supplementary Material

References

Associated Data

Supplementary Materials

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Table 1. Optimization of Pd(II)-Catalyzed Oxidative Heck Reaction^a.

General Procedure for the Preparation of Benzo[b]thiophene 1,1-Dioxides²²