Iridium-Catalyzed (Z)-Trialkylsilylation of Terminal Olefins

Abstract

A complex of commercial [Ir(OMe)(cod)]₂ and 4,4-di-tert-butyl-2,2-bipyridine (dtbpy) catalyzes the Z-selective, dehydrative silylation of terminal alkenes, but not 1,2-disubstituted alkenes, with triethylsilane or benzyldimethylsilane in THF at 40 °C. Yields and Z-stereoselectivity were significantly improved by 2-norbornene, in contrast with other sacrificial alkenes. The reaction is compatible with many functional groups including epoxides, ketones, amides, alcohols, esters, halides, ketals and silanes. a,b-Unsaturated esters were unreactive. The reaction probably proceeds through a Heck-type mechanism.

Introduction

The unique reactivity profile¹ of trialkylsilylalkenes (vinylsilanes) combined with their low environmental impact² and distinctive physical properties,³ has led to ever-widening roles for them as synthetic intermediates⁴ and as building blocks in numerous material science/polymer applications.⁵ Accordingly, a variety of procedures are extant for the preparation of vinylsilanes, inter alia, additions of vinyllithiums or Grignard reagents to silyl electrophiles,⁶ Wittig/Peterson olefinations,⁷ alkyne hydrosilyation,⁸ and Suzuki cross-coupling.^9,10 In more recent years, the direct silylation of alkenes mediated by transition metal catalysts,¹¹ e.g., iron,¹² cobalt,¹³ palladium,¹⁴ rhodium,¹⁵ ruthenium,¹⁶ iridium,¹⁷ and rhenium¹⁸ complexes, was introduced. Additionally, Kambe et al. reported the zirconocene catalyzed silylation of alkenes using chlorosilanes¹⁹ while Yorimitsu and Oshima developed an elegant silylation of terminal alkenes via Ni-catalyzed exchange with silacyclobutanes.²⁰ However, there are some important limitations associated with the stoichiometric and catalytic reactions. The former involve (i) strongly basic or harsh reaction conditions, (ii) multi-step processes, and/or (iii) give modest yields; the latter require (i) high alkene to silane ratios, (ii) conjugated or polyolefinic substrates, (iii) non-commercial reagents, and/or (iv) are E-selective. Herein, we offer a high yield Z-selective C-H silylation of terminal alkenes utilizing an iridium-dtbpy complex promoted by 2-norborene (eq 1) and some insights into the parameters that influence stereoselectivity.

(1)

Results and Discussion

Motivated by our recent iridium-catalyzed C-H functionalization/silylation of heteroarenes and the mechanistic understanding gained therein,²¹ we sought to extend this methodology to the more challenging case of isolated alkenes.^16,22 Initial attempts to silylate the model olefin 4-phenyl-1-butene 1 using [Ir(OMe)(cod)]₂/4,4-di-tert-butyl-2,2-bipyridine (dtbpy) (cod = cycloocta-1,5-diene)²³ and triethylsilane at either 80 °C or 40 °C in THF proved disappointing and gave rise to vinyl silane 2 in poor yield (Table 1, entries 1 and 2). The reversal of stereoselectivity towards the thermodynamically less favored Z-configuration at the lower temperature and the absence of aryl silylation, however, did not escape notice. Inclusion of mono- (entry 3), di- (entry 4), tri- (entry 5), and tetra-substituted (entry 6) olefins as sacrificial hydrogen repositories had little influence on the yield or stereoselectivity. In sharp contrast, 2-norbornene dramatically boosted yields (entries 7 and 8) and, in the latter case, the Z/E-ratio; at room temperature, the reaction was too sluggish to be useful (entry 9). Decreasing the amount of olefinic promoter and triethysilane resulted in a proportionate lessening of both conversion and Z-isomer (entry 10). Silylations also proceeded well in DME (entry 11), dioxane (entry 12), and even ether (entry 13), albeit with reduced stereoselectivity; toluene and dichloromethane were unsatisfactory (<5%). Commercial bicyclic (entries 14–16) and tricyclic (entry 17) promoters related to norbornene were less efficacious, except for a slight increase in the Z-selectivity in some instances. It is noteworthy that the dtbpy ligand also plays an important role by inhibiting the isomerization of olefin. Other similar ligands weren’t helpful (see Supporting Information).

TABLE 1.

Influence of promoters and reaction parameters on (Z)-selectivity and yield of 2^a

entry	promoter	temp (°C)	solvent	yield (%)b	Z:Ec
1	none	80	THF	<10	5:95d
2	none	40	THF	16	4:1
3		40	THF	<5	nde
4		40	THF	16	4:1
5		40	THF	<5	ndf
6		40	THF	<5	ndf
7		80	THF	91	2.5:1f
8		40	THF	92	9:1
9		23	THF	<5	nde,f
10		40	THF	60	5:1g
11		40	DME	90	8:1
12		40	dioxane	88	7:1
13		40	ether	91	3:1
14		40	THF	22	9:1
15		40	THF	21	10:1
16		40	THF	71	10:1
17		40	THF	20	4:1

^aReaction conditions: [Ir(OMe)(cod)]₂ (5 mol%), dtbpy (10 mol%), promoter (3 equiv, if used) and Et₃SiH (3 equiv) in THF for 2 h.

^bCombined yield.

^cMeasured by crude¹H NMR.

^dConducted for 15 h.

^end = not determined.

^fConducted for 24 h.

^gUsing 1.5 equivalents each of promoter and Et₃SiH.

The scope of this methodology was explored with a representative panel of alkenes (Table 2). Notably, only terminal alkenes proved reactive as illustrated by the nearly quantitative transformation of diene 3 to vinyl silane 4 (entry 1); all subsequent studies, therefore, were conduct with this in mind. Fortunately, the reaction conditions were compatible with a variety of functionality including, carbonate 5, methyl ester 7, and amide 9, which furnished 6 (entry 2), 8 (entry 3), 10 (entry 4), respectively, in good to excellent yields and Z-selectivities. Even the readily reduced epoxide 13 and methyl ketone 15 were well behaved and gave rise to the corresponding vinylsilanes 12 (entry 5) and 14 (entry 6). The smooth transformation of TBS ether 15, acetal 17 into 16 (entry 7) and 18 (entry 8) using commercial benzyldimethylsilane, instead of triethylsilane, demonstrates that other silyl moieties are accessible including those suitable for transition metal catalyzed cross-coupling reactions.²⁴

TABLE 2.

Trialkylsilylation of terminal alkenes^a

entry	alkene	silyl adduct	yield (%)b	Z:Ec
1	3	4	99	8:1
2	5	6	96	8:1
3	7	8	84	7:1
4	9	10	87	10:1
5	11	12	98	10:1
6	13	14	71	7:1
7	15	16	68	9:1
8	17	18	71	9:1
9	19	20	95	9:1
10	21	22	84	10:1
11	23	24	88	8:1
12	25	26	98	7:1
13	27	28	77	8:1
14	29	30	96	8:1
15	31	32	0	nad

^aReaction conditions: [Ir(OMe)(cod)]₂ (5 mol%), dtbpy (10 mol%), 2-norbornene (3 equiv) and R₃SiH (3 equiv) in THF for 2h at 40°C.

^bCombined isolated yield.

^cMeasured by 1H NMR.

^dna = not applicable.

Aryl groups were likewise good substrates and afforded to silylated benzoate 20, benzyl ether 22, 4-fluorophenyl 24, and 2-bromophenyl 26 beginning from 19 (entry 9), 21 (entry 10), 23 (entry 11), and 25 (entry 12), respectively. To our delight, even the free alcohol 27 generated silylated 28 (entry 13) in useful yield as did the related methyl ether 29 (entry 14). The corresponding allylic alcohol and methyl ether, on the other hand, produced complex product mixtures. NMR analysis of the crude mixtures suggested migration of the olefin might be a contributing factor. Also, conjugated alkenes, e.g., tert-butyl acrylate 31 (entry 15), produced numerous unidentified products and little of the desired Z-vinylsilane.

The details of the reaction mechanism are uncertain at the present time, but a tentative sequence similar to earlier proposals²⁵ is likely (Figure 1). Initial oxidative insertion of the iridium into the silane followed by addition to the more reactive 2-norbornyl olefin generates intermediate i. Heck-type addition²⁵ to the terminal alkene forms intermediate ii. Due to the unfavorable steric interactions present in iia, intermediate iib is likely the predominate conformation. Syn-β-hydride elimination from iib would lead to Z-vinylsilane and iridium-hydride complex iii. Reductive elimination of norbornane iv regenerates the catalyst and completes the catalytic cycle. Furthermore, this proposal highlights an underappreciated role for some so-called “sacrificial olefins” like 2-norbornene, i.e., they can also influence the stereoselectivity of the reaction and, thus, should be taken into consideration when selecting reagent combinations.

FIGURE 1.

Proposed mechanism of Ir-catalyzed trialkylsilylation showing influence of ligand

Conclusion

In summary, we describe a mild, Z-stereoselective dehydrogenative trialkylsilylation of terminal alkenes utilizing a commercial iridium catalyst. Additionally, we demonstrate that 2-norbornene strongly promotes the reaction and also influences its stereoselectivity. Extensions of these concepts will follow in due course.

Experimental Section

General Information

All reactions were carried out under an argon atmosphere. Anhydrous solvents were freshly distilled from sodium benzophenone ketyl, except for CH₂Cl₂, which was distilled from CaH₂. Extracts were dried over anhydrous Na₂SO₄ and then filtered prior to removal of all volatiles under reduced pressure. Unless otherwise noted, commercially available materials were used without further purification. [Ir(OMe)(COD)]₂ was purchased from Strem or Aldrich Chem. Co. Flash chromatography (FC) was performed using silica gel 60 (240–400 mesh). Thin layer chromatography was performed using precoated plates purchased (silica gel 60 PF254, 0.25 mm).

¹H and ¹³C NMR spectra were recorded in CDCl₃ unless stated otherwise. Chemical shifts (δ) are given in ppm relative to residual solvent (usually chloroform δ 7.26 for ¹H NMR or δ 77.23 for proton decoupled ¹³C NMR) and coupling constants (J) in Hz. Multiplicity is tabulated as s for singlet, d for doublet, t for triplet, q for quadruplet, and m for multiplet. The prefix app is applied in cases where the true multiplicity is unresolved and br when the signal in question is broadened..

General Procedure for Iridium-Catalyzed (Z)-Trialkylsilylation

A flame-dried Schlenk tube was charged with terminal alkene (0.2 mmol), [Ir(OMe)(cod)]₂ (6.6 mg, 0.01 mmol) and dtbpy (5.4 mg, 0.02 mmol), then evacuated and flushed with argon three times. Under a positive flow of argon, 2-norbornene (56 mg, 0.6 mmol) and dry THF (1 mL) were added. After stirring for 5 min, trialkylsilane (0.6 mmol) was added dropwise and the reaction mixture was stirred at 40 °C for 2h. The solvent was concentrated under reduced pressure and the residue was purified by flash chromatography using silica gel to give the vinylsilane generally as a Z/E-mixture. More extensive purification via PTLC was required to obtain the individual Z- and E-isomers.

Compound 2, combined yield 92%, Z/E = 9:1.

(Z)-Triethyl(4-phenylbut-1-enyl)silane

¹H NMR (300 MHz) δ 7.32-7.18 (m, 5H), 6.42 (dt, J = 14.1, 6.6 Hz, 1H), 5.44 (d, J = 14.1 Hz, 1H), 2.69 (t, J = 7.2 Hz, 2H), 2.46-2.38 (m, 2H), 0.93 (t, J = 7.5 Hz, 9H), 0.59 (q, J = 7.5 Hz, 6H); ¹³C NMR (75 MHz) δ 149.1, 142.1, 128.6, 128.6, 126.2, 126.1, 36.4, 36.3, 7.7, 4.9. HRMS (EI) calcd. for C₁₆H₂₆Si [M]⁺ m/z 246.1804, found 246.1805.

(E)-Triethyl(4-phenylbut-1-enyl)silane

¹H NMR (300 MHz) δ 7.30-7.17 (m, 5H), 6.07 (dt, J = 18.9 Hz, 6.3 Hz, 1H), 5.57 (d, J = 18.9 Hz, 1H), 2.72 (t, J = 7.5 Hz, 2H), 2.47-2.40 (m, 2H), 0.91 (t, J = 7.5 Hz, 9H), 0.53 (q, J = 7.5 Hz, 6H); ¹³C NMR (75 MHz) δ 147.7, 142.1, 128.7, 128.4, 126.7, 125.9, 39.0, 35.6, 7.6, 3.7.

Compound 4, combined yield 99%, Z/E =8:1.

1-Triethylsilyl-pentadeca-1(Z),12(Z)-diene

¹H NMR (300 MHz) δ 6.37 (dt, J = 13.8, 7.5 Hz, 1H), 5.39 (d, J = 13.8 Hz, 1H), 5.36-5.31 (m, 2H), 2.10-1.99 (m, 6H), 1.36-1.28 (m, 14H), 0.98-0.92 (m, 12H), 0.64-0.56 (m, 6H); ¹³C NMR (75 MHz) δ 150.6, 131.7, 129.6, 125.1, 34.3, 30.0 (2×C), 29.78 (2×C), 29.75, 29.6, 29.5, 27.3, 20.7, 14.6, 7.8, 4.9. HRMS (EI) calcd. for C₂₁H₄₂Si [M]⁺ m/z 322.3056, found 322.3063.

1-Triethylsilyl-pentadeca-1(E),12(Z)-diene

¹H NMR (300 MHz) δ 6.02 (dt, J = 18.6 Hz, 6.3 Hz, 1H), 5.52 (d, J = 18.6 Hz, 1H), 5.44-5.38 (m, 2H), 2.12-1.93 (m, 6H), 1.40-1.26 (m, 14H), 0.96-0.0.88 (m, 12H), 0.58-0.50 (m, 6H); ¹³C NMR (75 MHz) δ 149.1, 132.1, 129.6, 125.7, 37.3, 32.8, 29.9, 29.8, 29.7, 29.4, 29.3, 29.0, 25.8, 14.2, 7.6, 3.7.

Compound 6, combined yield 96%, Z/E = 8:1.

Ethyl 6-(triethylsilyl)hex-5(Z)-enyl carbonate

¹H NMR (300 MHz) δ 6.35 (dt, J = 14.4, 7.2 Hz, 1H), 5.42 (d, J = 14.4 Hz, 1H), 4.19 (q, J = 6.9 Hz, 2H), 4.14 (t, J = 6.6 Hz, 2H), 2.17-2.09 (m, 2H), 1.72- 1.66 (m, 2H), 1.52-1.44 (m, 2H), 1.31 (t, J = 6.6 Hz, 3H), 0.96-0.91 (m, 9H), 0.64-0.56 (m, 6H); ¹³C NMR (75 MHz) δ 155.5, 149.5, 126.1, 68.0, 64.1, 33.7, 28.5, 26.1, 14.5, 7.7, 4.9. HRMS (EI) calcd. for C₁₅H₃₁O₃Si [M+H]⁺ m/z 287.2042, found 287.2039.

(E)-Ethyl 6-(triethylsilyl)hex-5-enyl carbonate

¹H NMR (300 MHz) δ 6.00 (dt, J = 18.6, 6.3 Hz, 1H), 5.42 (d, J = 18.6 Hz, 1H), 4.19 (q, J = 7.2 Hz, 2H), 4.13 (t, J = 6.6 Hz, 2H), 2.18-2.12 (m, 2H), 1.71-1.62 (m, 2H), 1.52-1.46 (m, 2H), 1.31 (t, J = 7.2 Hz, 3H), 0.96-0.89 (m, 9H), 0.58-0.49 (m, 6H); ¹³C NMR (75 MHz) δ 155.5, 147.9, 126.7, 68.0, 64.1, 36.6, 28.3, 25.1, 14.5, 7.6, 3.7.

Compound 8, combined yield 84%, Z/E = 7:1.

Methyl 7-(triethylsilyl)hept-6(Z)-enoate

¹H NMR (300 MHz) δ 6.35 (dt, J = 14.4, 7.2 Hz, 1H), 5.41 (d, J = 14.1 Hz, 1H), 3.67 (s, 3H), 2.32 (t, J = 7.5 Hz, 1H), 2.15-2.07 (m, 2H), 1.70-1.60 (m, 2H), 1.45- 1.38 (m, 2H), 0.96-0.90 (m, 9H), 0.64-0.55 (m, 6H); ¹³CNMR (75MHz, CDCl₃): δ 174.4, 149.7, 125.9, 51.7, 34.2, 33.9, 29.5, 24.9, 7.8, 4.9. HRMS (EI) calcd. for C₁₄H₂₈O₂Si [M]⁺ m/z 256.1859, found 256.1855.

Methyl 7-(triethylsilyl)hept-6(E)-enoate

¹H NMR (300 MHz) δ 6.00 (dt, J = 18.6, 6.0 Hz, 1H), 5.55 (d, J = 18.6 Hz, 1H), 3.67 (s, 3H), 2.32 (t, J = 7.5 Hz, 1H), 2.17-2.10 (m, 2H), 1.69-1.58 (m, 2H), 1.48- 1.40 (m, 2H), 0.96-0.89 (m, 9H), 0.57-0.47 (m, 6H); ¹³C NMR (75 MHz) δ 174.4, 148.1, 126.4, 51.7, 36.8, 34.2, 28.4, 24.6, 7.6, 3.7.

Compound 10, combined yield 87%, Z/E =10:1.

N,N-Dibenzyl-7-(triethylsilyl)hept-6(Z)-enamide

¹H NMR (300 MHz) δ 7.39-7.14 (m, 10H), 6.35 (dt, J = 14.1, 7.2 Hz, 1H), 5.39 (d, J = 14.1 Hz, 1H), 4.61 (s, 2H), 4.44 (s, 2H), 2.43 (t, J = 7.2 Hz, 2H), 2.15-2.07 (m, 2H), 1.78-1.70 (m, 2H), 1.45-1.38 (m, 2H), 0.95-0.89 (m, 9H), 0.62-0.54 (m, 6H); ¹³C NMR (75 MHz) δ 173.7, 149.8, 137.7, 136.8, 129.2, 128.8, 128.5, 127.8, 127.6, 126.5, 125.7, 50.1, 48.3, 34.0, 33.4, 29.8, 25.4, 7.8, 4.9. HRMS (EI) calcd. for C₂₇H₄₀NOSi [M+H]⁺ m/z 422.2879, found 422.2877.

N,N-Dibenzyl-7-(triethylsilyl)hept-6(E)-enamide

¹H NMR (300 MHz) δ 7.39-7.14 (m, 10H), 6.00 (dt, J = 18.6, 6.0 Hz, 1H), 5.52 (d, J = 18.6 Hz, 1H), 4.60 (s, 2H), 4.44 (s, 2H), 2.43 (t, J = 7.2 Hz, 2H), 2.16-2.09 (m, 2H), 1.78-1.70 (m, 2H), 1.49-1.39 (m, 2H), 0.93-0.88 (m, 9H), 0.56-0.46 (m, 6H); ¹³C NMR (75 MHz) δ 173.8, 148.3, 137.7, 136.8, 129.2, 128.8, 128.5, 127.8, 127.6, 126.5, 126.2, 50.1, 48.2, 37.0, 33.3, 28.8, 25.2, 7.6, 3.7.

Compound 12, combined yield 98%, Z/E =10:1.

(Z)-Triethyl(8-(oxiran-2-yl)oct-1-enyl)silane

¹H NMR (300 MHz) δ 6.37 (dt, J = 14.1, 7.2 Hz, 1H), 5.39 (d, J = 14.1 Hz, 1H), 2.92-2.89 (m, 1H), 2.75 (dd, J = 3.9, 4.8 Hz, 1H), 2.47 (dd, J = 2.7, 4.8 Hz, 1H), 2.13-2.06 (m, 2H), 1.54-1.34 (m, 10H), 0.96-0.90 (m, 9H), 0.64-0.55 (m, 6H); ¹³C NMR (75 MHz) δ 150.4, 125.3, 52.6, 47.4, 34.2, 32.7, 29.9, 29.6, 29.5, 26.1, 7.8, 4.9. HRMS (EI) calcd. for C₁₆H₃₂OSi [M]⁺ m/z 268.2222, found 268.2222.

(E)-Triethyl(8-(oxiran-2-yl)oct-1-enyl)silane

¹H NMR (300 MHz) δ 6.02 (dt, J = 18.9 Hz, 6.3Hz, 1H), 5.53 (d, J = 18.9 Hz, 1H), 2.92-2.88 (m, 1H), 2.75 (dd, J = 3.9, 4.8 Hz, 1H), 2.47 (dd, J = 2.7, 4.8 Hz, 1H), 2.15-2.08 (m, 2H), 1.54-1.34 (m, 10H), 0.95-0.89 (m, 9H), 0.58-0.50 (m, 6H); ¹³C NMR (75 MHz) δ 148.8, 125.8, 52.6, 47.4, 37.2, 32.7, 29.5, 29.2, 28.9, 26.1, 7.6, 3.7.

Compound 14, combined yield 71%, Z/E = 7:1.

6-(Triethylsilyl)hex-5(Z)-en-2-one, 62% yield following PTLC separation. ¹H NMR (300 MHz) δ 6.31 (dt, J = 14.1, 7.2 Hz, 1H), 5.45 (d, J = 14.1 Hz, 1H), 2.53-2.48 (m, 2H), 2.40-2.34 (m, 2H), 2.15 (s, 3H), 1.49-1.42 (m, 2H), 0.96-0.90 (m, 9H), 0.65-0.57 (m, 6H); ¹³C NMR (75 MHz) δ 208.3, 147.9, 127.0, 43.8, 30.2, 28.3, 7.7, 4.8. HRMS (EI) calcd. for C₁₂H₂₄OSi [M]⁺ m/z 212.1596, found 212.1599.

6-(Triethylsilyl)hex-5(E)-en-2-one, 9% yield following PTLC separation. ¹H NMR (300 MHz) δ 6.01 (dt, J = 18.6, 6.3 Hz, 1H), 5.57 (d, J = 18.6 Hz, 1H), 2.56-2.52 (m, 2H), 2.43-2.36 (m, 2H), 2.15 (s, 3H), 1.49-1.42 (m, 2H), 0.93-0.88 (m, 9H), 0.57-0.49 (m, 6H); ¹³C NMR (75 MHz) δ 208.6, 146.3, 127.1, 42.9, 31.1, 30.2, 7.6, 3.6.

Compound 16, combined yield 71%, Z/E =7:1.

(Z)-Benzyl(6-(tert-butyldimethylsilyloxy)hex-1-enyl)dimethylsilane

¹H NMR (300 MHz) δ 7.25- 7.18 (m, 2H), 7.09-7.00 (m, 3H), 6.33 (dt, J = 14.1, 7.5Hz, 1H), 5.44 (d, J = 14.1 Hz, 1H), 3.59 (t, J = 6.3 Hz, 1H), 2.15 (s, 2H), 2.09-2.02 (m, 2H), 1.53-1.46 (m, 2H), 1.41-1.35 (m, 2H), 0.90 (s, 9H), 0.09 (s, 6H), 0.04 (s, 6H); ¹³C NMR (75 MHz) δ 150.4, 140.4, 128.4, 128.3, 127.0, 124.1, 63.3, 33.7, 32.7, 26.9, 26.2, 26.1, 18.6, −1.4, −5.1. HRMS (EI) calcd. for C₂₁H₃₉Si₂ [M+H]⁺ m/z 363.2539, found 363.2541.

(E)-Benzyl(6-(tert-butyldimethylsilyloxy)hex-1-enyl)dimethylsilane

¹H NMR (300 MHz) δ 7.25-7.18 (m, 2H), 7.09-7.00 (m, 3H), 5.99 (dt, J = 18.9, 7.5 Hz, 1H), 5.58 (d, J = 18.9 Hz, 1H), 3.60 (t, J = 6.3 Hz, 1H), 2.10 (s, 2H), 2.12-2.08 (m, 2H), 1.53-1.47 (m, 2H), 1.45-1.40 (m, 2H), 0.05 (s, 9H), 0.01 (s, 6H), 0.04 (s, 6H); ¹³C NMR (75 MHz) δ 148.6, 140.4, 128.4, 128.2, 127.9, 124.0, 63.3, 36.7, 32.5, 26.4, 26.2, 18.6, −3.1, −5.0.

Compound 18, combined yield 71%, Z/E =7:1.

(Z)-Benzyldimethyl(4-(2-methyl-1,3-dioxolan-2-yl)but-1-enyl)silane

¹H NMR (300 MHz) δ 7.23-7.18 (m, 2H), 7.09-7.00 (m, 3H), 6.33 (dt, J = 14.1, 7.2 Hz, 1H), 5.45 (d, J = 14.1 Hz, 1H), 3.98-3.86 (m, 4H), 2.17 (s, 2H), 2.17-2.10 (m, 2H), 1.68-1.63 (m, 2H), 1.30 (s, 3H), 0.11 (s, 6H); ¹³C NMR (75 MHz) δ 149.6, 140.3, 128.4, 128.3, 127.2, 124.1, 109.9, 64.9, 39.1, 28.7, 26.9, 24.1, −1.5. HRMS (EI) calcd. for C₁₇H₂₆O₂Si [M]⁺ m/z 290.1702, found 290.1704.

(E)-Benzyldimethyl(4-(2-methyl-1,3-dioxolan-2-yl)but-1-enyl)silane

¹H NMR (300 MHz) δ 7.22- 7.17 (m, 2H), 7.08-6.97 (m, 3H), 6.02 (dt, J = 18.6, 6.3 Hz, 1H), 5.61 (d, J = 18.6 Hz, 1H), 3.97-3.88 (m, 4H), 2.25-2.17 (m, 2H), 2.10 (s, 2H), 1.75-1.70 (m, 2H), 1.32 (s, 3H), 0.01 (s, 6H); ¹³C NMR (75 MHz) δ 148.1, 140.4, 128.5, 128.2, 127.7, 124.1, 110.0, 64.9, 38.2, 31.4, 26.4, 24.2, −3.1.

Compound 20, combined yield 95%, Z/E =9:1.

(Z)-5-(Triethylsilyl)pent-4-enyl benzoate

¹H NMR (300 MHz) δ 8.07-8.04 (m, 2H), 7.56-7.53 (m, 1H), 7.47-7.41 (m, 2H), 6.41(dt, J = 14.1, 7.2 Hz, 1H), 5.48 (d, J = 14.1Hz, 1H), 4.34 (t, J = 6.3 Hz, 2H), 2.32-2.25 (m, 2H), 1.91-1.82 (m, 2H), 0.95-0.90 (m, 9H), 0.65-0.57 (m, 6H); ¹³C NMR (75 MHz) δ 166.9, 148.6, 133.1, 130.6, 129.8, 128.5, 126.8, 64.8, 30.8, 29.1, 7.7, 4.9. HRMS (EI) calcd. for C₁₈H₂₈O₂Si [M]⁺ m/z 304.1859, found 304.1874.

(E)-(6-(Benzyloxy)hex-1-enyl)triethylsilane

¹H NMR (300 MHz) δ 8.07-8.04 (m, 2H), 7.58-7.53 (m, 1H), 7.47-7.42 (m, 2H), 6.41(dt, J = 18.6, 6.3 Hz, 1H), 5.62 (d, J = 18.6 Hz, 1H), 4.33 (t, J = 6.6 Hz, 2H), 2.33-2.26 (m, 2H), 1.94-1.84 (m, 2H), 0.97-0.90 (m, 9H), 0.58-0.50 (m, 6H); ¹³C NMR (75 MHz, CDCl₃) δ 166.9, 147.0, 133.1, 130.6, 129.8, 128.5, 127.3, 64.7, 33.5, 28.0, 7.6, 3.7.

Compound 22, combined yield 84%, Z/E = 10:1.

(Z)-(6-(Benzyloxy)hex-1-enyl)triethylsilane

¹H NMR (300 MHz) δ 7.35-7.26 (m, 5H), 6.36 (dt, J = 14.1, 7.5 Hz, 1H), 5.40 (d, J = 14.1 Hz, 1H), 4.51 (s, 2H), 3.48 (t, J = 6.6 Hz, 2H), 2.16-2.09 (m, 2H), 1.67-1.60 (m, 2H), 1.49-1.44 (m, 2H), 0.96-0.90 (m, 9H), 0.64-0.55 (m, 6H); ¹³C NMR (75 MHz) δ 150.1, 138.8, 128.6, 127.8, 127.7, 125.6, 73.1, 70.5, 34.0, 29.7, 26.6, 7.8, 4.9. HRMS (EI) calcd. for C₁₉H₃₁OSi [M+H]⁺ m/z 303.2144, found 303.2160.

(E)-(6-(Benzyloxy)hex-1-enyl)triethylsilane

¹H NMR (300 MHz) δ 7.35-7.26 (m, 5H), 6.02 (dt, J = 18.6 Hz, 6.3 Hz, 1H), 5.40 (d, J = 18.6 Hz, 1H), 4.51 (s, 2H), 3.48 (t, J = 6.6 Hz, 2H), 2.17-2.11 (m, 2H), 1.66-1.58 (m, 2H), 1.51-1.45 (m, 2H), 0.95-0.90 (m, 9H), 0.59-0.50 (m, 6H); ¹³C NMR (75 MHz) δ 148.5, 138.9, 128.6, 127.8, 127.7, 126.2, 73.0, 70.5, 37.0, 29.4, 25.6, 7.6, 3.7.

Compound 24, combined yield 88%, Z/E =8:1.

(Z)-Triethyl(4-(4-fluorophenyl)but-1-enyl)silane

¹H NMR (300 MHz) δ 7.15-7.10 (m, 2H), 6.99-6.94 (m, 2H), 6.39 (dt, J = 14.1, 7.2 Hz, 1H), 5.45 (d, J = 14.1 Hz, 1H), 2.66 (t, J = 7.5 Hz, 2H), 2.42-2.35 (m, 2H), 0.95-0.88 (m, 9H), 0.62-0.54 (m, 6H); ¹³C NMR (75 MHz) δ 163.1, 159.9, 148.8, 137.65, 137.6, 130.0, 129.9, 126.5, 115.4, 115.1, 36.3, 35.5, 7.7, 4.9. HRMS (EI) calcd. for C₁₆H₂₅FSi [M]⁺ m/z 246.1710, found 264.1715.

(E)-Triethyl(4-(4-fluorophenyl)but-1-enyl)silane

¹H NMR (300 MHz) δ 7.14-7.09 (m, 2H), 6.98-6.92 (m, 1H), 6.01 (dt, J = 18.9 Hz, 6.0 Hz, 1H), 5.56 (d, J = 18.9 Hz, 1H), 2.69 (t, J = 7.2 Hz, 2H), 2.44-2.37 (m, 2H), 0.93-0.88 (m, 9H), 0.57-0.49 (m, 6H); ¹³C NMR (75 MHz) δ 163.0, 159.8, 147.3, 137.75, 137.71, 130.0, 129.9, 127.1, 115.3, 115.0, 39.0, 34.7, 7.6, 3.7.

Compound 26, combined yield 88%, Z/E = 7:1.

(Z)-(4-(2-Bromophenyl)but-1-enyl)triethylsilane

¹H NMR (300 MHz) δ 7.55-7.52 (m, 1H), 7.24-7.21 (m, 2H), 7.09-7.03 (m, 1H), 6.43 (dt, J = 14.1, 7.2 Hz, 1H), 5.46 (d, J = 14.1 Hz, 1H), 2.81 (t, J = 7.5 Hz, 2H), 2.46-2.38 (m, 2H), 0.96-0.89 (m, 9H), 0.63-0.55 (m, 6H); ¹³C NMR (75 MHz) δ 148.6, 141.3, 133.0, 130.7, 127.8, 127.6, 126.6, 124.6, 36.5, 34.4, 7.7, 4.8. HRMS (EI) calcd. for C₁₆H₂₅BrSi [M]⁺ m/z 324.0909, found 324.0906.

(E)-(4-(2-Bromophenyl)but-1-enyl)triethylsilane

¹H NMR (300 MHz) δ 7.52 (d, J = 7.8 Hz, 1H), 7.24-7.20 (m, 2H), 7.07-7.02 (m, 1H), 6.07 (dt, J = 18.6 Hz, 6.3 Hz, 1H), 5.57 (d, J = 18.6 Hz, 1H), 2.84 (t, J = 7.5 Hz, 2H), 2.46-2.40 (m, 2H), 0.93-0.88 (m, 9H), 0.57-0.50 (m, 6H); ¹³C NMR (75 MHz) δ 147.0, 141.3, 132.9, 130.7, 127.7, 127.5, 127.2, 124.6, 37.2, 35.8, 7.6, 3.7.

Compound 28, combined yield 77%, Z/E = 8:1.

(Z)-Triethyl(4-hydroxyl-4-phenylbut-1-enyl)silane, 68% yield following PTLC separation. ¹H NMR (300 MHz) δ 7.38-7.26 (m, 5H), 6.41 (dt, J = 14.1, 7.2 Hz, 1H), 5.64 (d, J = 14.1 Hz, 1H), 4.77-4.73 (m, 1H), 2.61-2.55 (m, 2H), 2.03-2.00 (m, 1H), 0.96-0.91 (m, 9H), 0.66-0.58 (m, 6H); ¹³C NMR (75 MHz) δ 145.1, 144.2, 129.9, 128.7, 127.8, 126.0, 74.1, 43.9, 7.7, 4.8. HRMS (EI) calcd. for C₁₆H₂₆OSi [M]⁺ m/z 262.1753, found 262.1751.

(E)-Triethyl(4-hydroxyl-4-phenylbut-1-enyl)silane, 8% yield following PTLC separation. ¹H NMR (300 MHz) δ 7.36-7.24 (m, 5H), 6.01 (dt, J = 18.6 Hz, 6.3 Hz, 1H), 5.71 (d, J = 18.6 Hz, 1H), 4.78-4.73 (m, 1H), 2.62-2.55 (m, 2H), 2.03-2.02 (m, 1H), 0.93-0.88 (m, 9H), 0.58-0.50 (m, 6H); ¹³C NMR (75 MHz) δ 144.1, 143.7, 131.6, 128.6, 127.7, 126.0, 73.4, 47.4, 7.6, 3.6.

Compound 30, combined yield 96%, Z/E = 8:1.

(Z)-Triethyl(4-methoxy-4-phenylbut-1-enyl)silane, 85% yield following PTLC separation. ¹H NMR (300 MHz) δ 7.39-7.26 (m, 5H), 6.36 (dt, J = 14.4 Hz, 7.2 Hz, 1H), 5.50 (d, J = 14.4 Hz, 1H), 4.14 (t, J = 6.6 Hz, 1H), 3.22 (s, 3H), 2.67-2.59 (m, 2H), 2.49-2.40 (m, 2H), 0.93-0.88 (m, 9H), 0.61-0.53 (m, 6H); ¹³C NMR (75 MHz) δ 145.6, 141.9, 128.6, 127.9, 127.8, 126.9, 84.2, 56.9, 42.5, 7.7, 4.8. HRMS (EI) cald. for C₁₇H₂₈OSi [M]⁺ m/z 276.1909, found 276.1907.

(E)-Triethyl(4-methoxy-4-phenylbut-1-enyl)silane, yield 10% following PTLC separation. ¹H NMR (300 MHz) δ 7.36-7.24 (m, 5H), 5.95 (dt, J = 18.6 Hz, 6.3Hz, 1H), 5.55 (d, J = 18.6 Hz, 1H), 4.14 (t, J = 6.6 Hz, 1H), 3.22 (s, 3H), 2.67-2.59 (m, 2H), 2.49-2.40 (m, 2H), 0.90-0.85 (m, 9H), 0.54-0.46 (m, 6H); ¹³C NMR (75 MHz) δ 144.1, 141.9, 129.3, 128.5, 127.7, 127.0, 84.0, 56.9, 45.9, 7.5, 3.6.