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Logo of nihpaAbout Author manuscriptsSubmit a manuscriptHHS Public Access; Author Manuscript; Accepted for publication in peer reviewed journal;
 
Tetrahedron. Author manuscript; available in PMC 2010 July 13.
Published in final edited form as:
Tetrahedron. 2009 July 11; 65(28): 5608–5613.
doi:  10.1016/j.tet.2009.04.016
PMCID: PMC2902782
NIHMSID: NIHMS126651

Silylene oxonium ylides: di-tert-butylsilylene insertion into C—O bonds

Abstract

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Allylic ethers undergo insertions of silylenes into C—O bonds to form allylic silanes. Silylene insertion into C—O acetal bonds was also observed. Formation of silylene ylide intermediates led to [1,2]-Stevens rearrangement products as well as [2,3]-sigmatropic products depending upon the steric environment of the starting allylic ether.

Keywords: Silylene, Oxonium ylide, Allylic Silanes

1. Introduction

Oxonium ylides are characterized by their instability and high reactivity. Common oxonium carbene ylide reactions involve [1,2]-Stevens rearrangements1 (Scheme 1) and [2,3]-sigmatropic rearrangements (Scheme 2) to form synthetically useful products.2-11 Analogous oxonium silylene ylides have also been observed.12-15 Allylic ethers subjected to photolytically generated silylenes most often formed silacyclopropane intermediates instead of oxonium ylides.14 For reactions that are thought to proceed through oxonium silylene ylide intermediates, [2,3]-sigmatropic products were observed instead of [1,2]-Stevens rearrangement products. Previously, we reported preliminary results of a metal-catalyzed silylene insertion into allylic ethers yielding formal [1,2]-Stevens rearrangement products.16 In this paper, we expand upon the method wherein metal-catalyzed silylene transfer to allylic ethers produces allylic silanes by way of silylene insertion. A mechanism for the insertion of silylene into a C—O bond is postulated whereby the allylic silanes are thought to be generated through a diradical intermediate, creating formal [1,2]-Stevens rearrangement or [2,3]-sigmatropic rearrangement products.

2. Results and Discussion

2.1 Substrate Scope

Insertion into allylic C—O bonds was first observed upon treatment of benzyl-protected allylic alcohols with a silylene source. When allylic ether 9 was treated with cyclohexene silacyclopropane (10) and silver trifluoroacetate, allylic disilane 11 was formed in 66% yield (eq 1). A disilyl hydride by-product (12) was also observed in 29% yield.

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Insertion of a single silicon unit into the allylic C—O bond was observed when the allylic ether contained substitution at the α-position. Allylic ether 13 provided allylic silane 14 in 74% yield and disilyl hydride by-product 12 in 20% yield (eq 2). The observation that a single silicon unit had inserted into allylic ether 13 suggests that steric effects contribute to the outcome of insertions of silylenes into allylic C—O bonds.

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A control experiment provided evidence that in the formation of allylic disilanes, the two silicon units are inserted simultaneously. Allylic silane 15, bearing a single silicon unit, was subjected to the reaction conditions (eq 3). After 12 h of monitoring by 1H NMR spectroscopy, starting material was observed unchanged. A lack of insertion of a second silylene group suggests that both silicon units are inserted concurrently, instead of sequentially.

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Attempts were made to optimize the silylene insertion reaction to reduce the formation of disilyl by-product 12. When the insertion reaction conditions employed a silver salt as the catalyst, disilyl-hydride by-product 12 was observed in 20-40% yield for various silylene insertion reactions. Efforts to separate the disilyl by-product from the desired allylic silanes were problematic due to the similar polarity of the two compounds. Because large amounts of by-product 12 were observed with several protecting groups and different substitution patterns at the α-position of the allylic ether, formation of the disilane by-product 12 appeared to be independent of electronic and steric factors. A mechanism for generation of disilane 12, illustrated in Scheme 3, could be envisioned from tetra-t-butyldisilene 19 forming by way of dimerization of free silylene.17, 18 Coordination of the disilene to the oxygen atom of 18 to form disilyl ylide intermediate 20 and subsequent elimination of diene 21 would provide disilane 12. Small vinyl peaks identified in the 1H NMR spectra of di-tert-butylsilylene insertion reaction mixtures were speculated to be characteristic of diene by-products such as 21.

A catalyst screen was conducted in hopes of suppressing the formation of disilyl by-product 12. Treatment of allylic ether 9 with cyclohexene silacyclopropane (10) and copper (I) triflate led to allylic silane 15 in 81% yield (eq 4). Disilyl by-product 12 was not observed. Copper-mediated silylene insertion reactions requried longer reaction times but provided cleaner products in better yields than silver-mediated reactions.

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Under the optimized conditions, cyclic allylic ethers were also shown to undergo silylene insertion. Trisubstituted cyclic allylic ether 22 was treated to the reaction conditions to provide allylic silane 23 in 81% yield (Scheme 4). Pivaloate 24 underwent silylene insertion as well (Scheme 4).

Unhindered alkenes undergo silylene transfer to form isomeric mixtures of products. Geminally disubstituted allylic ether 26 provided allylic silane 27 as a 50:50 E/Z isomeric mixture. Transposition of the double bond suggests that terminal alkenes undergo silylene insertion by way of a formal [2,3]-sigmatropic reaction, not a direct insertion. Treatment of allylic ether 28 to the reaction conditions led to an inseparable 67:33 E/Z isomeric mixture of allylic silane product 29 (Scheme 5). Partial isomerization of the alkene bond suggests that allylic ether 28 underwent both allylic transposition and direct insertion.

Various allylic ethers were treated to the reaction conditions, but not all underwent silylene insertion. Monosubstituted alkene 30 formed silacyclopropane 31 as the sole product of di-tert-butylsilylene transfer, suggesting that silacyclopropanes are not intermediates along the reaction pathway to C—O insertion products (eq 5). Silyl ether protecting groups did not undergo C—O insertion (eq 6). This experiment suggests that the initial complexation of the silylene unit to the allylic oxygen to form the oxonium silylene ylide is important in the insertion reaction, and that this step is sensitive to steric effects.

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Silylene insertion was expanded beyond allylic substrates to other varieties of C—O bonds. Benzylic C—O bonds underwent double silylene insertion when subjected to reaction conditions (eq 7). The higher temperatures and longer reaction times demonstrate that the benzylic C—O bond is less favorable towards silylene insertion than an allylic C—O bond. This rate difference does not follow the C—O bond dissociation energies, where insertion into a benzylic C—O bond would appear to be more favorable than an allylic C—O bond.19 Acetals were also found to undergo silylene insertion. Benzaldehyde dimethyl acetal (35) inserted one silylene unit into a benzylic C—O bond to form benzylic silane 36 in 60% yield. Insertion of a silylene unit into propionaldehyde diethyl acetal 37 demonstrated that unsaturation was not necessary for the insertion reaction to proceed (Table 1). Insertion into an acetal C—O bond lacking unsaturation in the carbon backbone suggests that C—O bonds that form stabilized radicals upon homolysis may be generally susceptible to silylene insertion.

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2.2 Mechanistic Experiments

Alteration of the electronic properties of the starting allylic ethers influenced the rate of silylene insertion. Electron-poor (trifluoromethyl)benzyl ether 39 and electron-rich methoxybenzyl ether 41 were subjected to reaction conditions and the rates of the reaction were compared to the reaction rate for benzylic ether 9 (Scheme 6). Electron-withdrawing groups at the para-position on the aryl protecting group led to an increase in the rate of silylene insertion. The substrate with an electron-donating group residing in the same position did not go to completion without heating.

A crossover experiment provided further insight into the reaction mechanism of silylene insertion. Treatment of benzyl-protected allylic ether 43 and p-xylyl-protected allylic ether 44 to reaction conditions could have provided four possible allylic silane products (Scheme 7). Upon isolation of the products, only two allylic silanes (45 and 46) were observed. The lack of formation of crossover products 47 and 48 in the reaction suggests that once the oxonium silylene ylide is formed, insertion occurs either concertedly or through a closely associated ion or radical pair.

Reactions of diastereomeric cyclic allylic ethers illuminated the stereochemistry of silylene insertion. A 1:1 stereoisomeric mixture of cyclic allylic ether 49 was treated to the reaction conditions to yield a 1:1 mixture of allylic silane 50 (eq 8). When the cis isomer of the allylic ether (51) underwent silylene insertion, only the cis diastereomer of the product was formed, but erosion of enantioselectivity was observed (eq 9). Through X-ray crystallography and analysis of chiral esters, allylic silanes 52 and 52′ were shown to conserve facial selectivity.16 The loss of enantioselectivity can be explained by the production of allylic silane 52′ being formed concurrently with allylic silane 52. Retention of facial selectivity appears to be consistent with a [1,2]-Stevens rearrangement pathway20-22 with some allylic transposition23 occurring.

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A mechanism that is consistent with our mechanistic experiments is proposed in Scheme 8. In a reversible first step, the nucleophilic oxygen atom attacks the electrophilic metal silylenoid complex24 to form ylide 55 or 56. Correlation to the analogous carbene systems suggest that silylene ylide 56 is in a dynamic equilibrium with metal-associated ylide 55.6 The carbon—oxygen bond is then broken and a closely dissociated radical pair (or ion pair) is formed. The diradical intermediate 57 can then recombine to provide formal [1,2]-Stevens rearrangement products or [2,3]-sigmatropic rearrangement products depending upon the steric congestion of the carbon—carbon double bond.20-23 When the terminal end of the allylic ether is not hindered, the formal [2,3]-sigmatropic rearrangement occurs to provide allylic silane transposition products, whereas when this pathway is blocked, formal [1,2]-Stevens products are observed (Scheme 8). Migration of the silylene unit occurs on the same face and consequently conserves diastereoselectivity.

3. Conclusion

Silylene insertion into allylic ethers was observed. Both silver and copper catalysts promoted the reaction, although silver salts led to formation of a disilyl hydride by-product. Acetal C-O bonds also underwent silylene insertion. Allylic ethers containing sterically hindered double bonds led to formal [1,2]-Stevens rearrangement products, while [2,3]-sigmatropic rearrangement products were observed for less bulky alkenes.

4. Experimental

General

1H NMR and 13C NMR spectra were recorded at room temperature using Bruker DRX 400, DRX 500, or DRX 600 spectrometers, as indicated. The data are reported as follows: chemical shift in ppm from an internal tetramethylsilane standard on the δ scale, multiplicity (br = broad, s = singlet, d = doublet, t = triplet, q = quartet, m = multiplet), coupling constants (Hz), and integration. Due to difficulties with purification for certain products, only characteristic peaks are listed in tabulated 1H NMR spectroscopic data. High resolution mass spectra were acquired on a VG analytical 7070E or Fisions Autospec spectrometer, and were obtained by peak matching. Microanalyses were performed by Atlantic Microlabs, Norcross, GA. Analytical thin layer chromatography was performed on EM reagents 0.25 mm silica gel 60-F plates. Liquid chromatography was performed using forced flow (flash chromatography) of the indicated solvent system on EM reagents silica gel (SiO2) 60 (230-400). Silacyclopropanes were stored and manipulated in an Innovative Technologies nitrogen-atmosphere dry box. All reactions were performed under an atmosphere of nitrogen or argon in glassware that had been flame-dried under a stream of nitrogen or under vacuum. Solvents were distilled or filtered through alumina before use. Sodium hydride and potassium hydride were used dry and weighed in a nitrogen-atmosphere dry box. Cyclohexene silacyclopropane (10) was constructed by known methods.25, 26 Additional experiments were reported previously.16

Disilylhydride 12

To a Schlenck flask was added allylic ether 9 (0.088 g, 0.50 mmol), silacyclopropane 10 (0.235 g, 1.05 mmol), AgO2CCF3 (0.001 g, 0.005 mmol) and 3 mL of toluene. The brown solution was then placed under an Ar atmosphere and allowed to stir for 3 h, at which point the mixture was concentrated in vacuo. The resultant yellow oil was purified by flash chromatography (hexanes) to afford 12 (0.057 g, 29%) as a colorless oil: 1H NMR (500 MHz, CDCl3) δ 7.30–7.41 (m, 5H), 5.08 (s, 2H), 3.72 (s, 1H), 1.24 (s, 18H), 1.21 (s, 18H); 13C NMR (125 MHz, CDCl3) δ 141.0, 128.1, 126.9, 126.8, 67.2, 31.4, 29.1, 24.0, 20.8; IR (thin film) 3030, 2856, 2073, 1362, 1070, 815 cm-1; HRMS (GCMS) m / z calcd for C23H44NaOSi2 (M + Na)+ 415.2828, found 415.2830. Anal. Calcd for C23H44OSi2: C, 70.33; H, 11.29. Found: C, 70.77; H, 11.65.

Representative procedure for the synthesis of aryl-protected allylic alcohols (allylic ether 22)

To a 0 °C solution of NaH (0.808 g, 33.7 mmol) in 86 mL of THF was added BnBr (2.92 mL, 24.6 mmol), followed by addition of 3-methyl-2-cyclohexen-1-ol (2.91 g, 25.9 mmol) dropwise. The reaction mixture was warmed to ambient temperature and maintained for 12 h. The solution was diluted with 30 mL of H2O. The layers were separated, and the aqueous layer was extracted with hexanes (3 × 30 mL). The combined organic layers were washed with 30 mL of saturated aqueous NaCl, dried (Na2SO4), filtered, and concentrated in vacuo. The resultant yellow oil was purified by flash chromatography (98:2 hexanes:EtOAc) to afford 22 (2.78 g, 52%) as a colorless oil: 1H NMR (400 MHz, CDCl3) δ 7.26–7.39 (m, 5H), 5.58–5.59 (m, 1H), 4.61 (d, J = 12.0, 1H), 4.55 (d, J = 12.0, 1H), 3.95–3.97 (m, 1H), 1.72–1.97 (m, 5H), 1.71 (s, 3H), 1.25–1.28 (m, 1H); 13C NMR (125 MHz, CDCl3) δ 139.2, 139.1, 128.4, 127.7, 127.4, 122.2, 72.7, 70.1, 30.3, 28.0, 23.8, 19.4. 1H and 13C NMR spectroscopic data matched those previously reported.27

Representative procedure for the synthesis of allylic silanes (allylic silane 23)

To a Schlenck flask was added allylic ether 22 (0.202 g, 1.00 mmol), silacyclopropane 10 (0.270 g, 1.20 mmol), CuOTf·PhMe (0.026 g, 0.050 mmol, 2:1 complex) and 7 mL of toluene. The brown solution was then placed under an Ar atmosphere and allowed to stir for 12 h, at which point the mixture was concentrated in vacuo. The resultant yellow oil was purified by flash chromatography (hexanes) to afford 23 (0.278 g, 81%) as a colorless oil: 1H NMR (400 MHz, CDCl3) δ 7.24–7.40 (m, 5H), 5.54–5.55 (m, 1H), 4.97–4.98 (m, 2H), 2.16–2.17 (m, 1H), 1.84–1.97 (m, 4H), 1.66–1.75 (m, 1H), 1.64 (s, 3H), 1.40–1.45 (m, 1H), 1.10 (s, 18H); 13C NMR (125 MHz, CDCl3) δ 142.0, 131.9, 128.4, 126.7, 125.8, 122.4, 66.0, 30.2, 29.3, 29.1, 24.5, 24.4, 22.8, 22.7; IR (thin film) 2931, 2856, 1454, 1082, 910, 735 cm-1; HRMS (APCI) m / z calcd for C22H36NaOSi CR(M + Na)+ 367.2433, found 367.2437.

Allylic ether 28

The representative procedure for the synthesis of aryl-protected allylic alcohols was followed using trans-3-methyl-3-penten-2-ol (0.642 g, 6.40 mmol), NaH (0.200 g, 8.32 mmol), BnBr (0.72 mL, 6.1 mmol), and 22 mL of dry THF for 12 h. Purification by flash chromatography (95:5 hexanes:EtOAc) afforded 28 (0.730 g, 63%) as a colorless oil: 1H NMR (500 MHz, CDCl3) δ 7.19–7.35 (m, 5H), 5.46 (q, J = 6.0, 1H), 4.44 (d, J = 11.9, 1H), 4.24 (d, J = 11.9, 1H), 3.86 (q, J = 6.5, 1H), 1.66 (d, J = 6.5, 3H), 1.62 (s, 3H), 1.26 (d, J = 6.5, 3H); 13C NMR (125 MHz, CDCl3) δ 139.1, 136.6, 128.4, 127.8, 127.4, 122.0, 80.6, 69.6, 20.3, 13.2, 10.2; IR (thin film) 2977, 2861, 1454, 1204, 1093, 734 cm-1; HRMS (ESI) m / z calcd for C13H18NaO (M + Na)+ 213.1255, found 213.1255. Anal. Calcd for C13H18O: C, 82.06; H, 9.53. Found: C, 81.62; H, 9.39.

Allylic silane 29

The representative procedure for the synthesis of allylic silanes was followed using allylic ether 28 (0.190 g, 1.00 mmol), silacyclopropane 10 (0.337 g, 1.50 mmol), CuOTf·PhMe (0.026 g, 0.050 mmol, 2:1 complex), and 6.7 mL of toluene for 12 h. Purification by flash chromatography (99:1 hexanes:EtOAc) afforded an inseparable 67:33 E/Z isomeric mixture of 29 (0.222 g, 67%) as a colorless oil: 1H NMR (500 MHz, CDCl3) δ 7.24–7.35 (m, 12.5H), 5.24–5.26 (m, 1.5H), 5.10–5.11 (m, 1H), 4.96–4.98 (m, 5H), 2.65–2.67 (m, 1H), 2.10–2.12 (1.5H), 1.81 (s, 3H), 1.67 (s, 4.5H), 1.62–1.63 (m, 3H), 1.56–1.58 (m, 4.5H), 1.31–1.33 (m, 4.5H), 1.26–1.28 (m, 3H), 1.12 (br s, 45H); 13C NMR (125 MHz, CDCl3) δ 141.8, 141.5, 140.1, 139.9, 128.14, 128.13, 126.63, 126.62, 125.61, 125.58, 117.7, 116.8, 66.0, 65.7, 30.6, 29.8, 29.2, 29.1, 28.8, 23.6, 23.3, 23.0, 22.9, 22.8, 22.5, 18.0, 16.4, 16.3, 13.4, 13.7; IR (thin film) 2966, 2858, 1473, 1376, 1113, 821 cm-1; HRMS (APCI) m / z calcd for C21H36NaOSi (M + Na)+ 355.2433, found 355.2440. Anal. Calcd for C21H36OSi: C, 75.84; H, 10.91. Found: C, 76.08; H, 11.08.

Benzylic silane 36

To a J. Young NMR tube was added benzaldehyde dimethyl acetal (35) (19 μL, 0.125 mmol), silacyclopropane 10 (0.034 g, 0.150 mmol), AgO2CCF3 (0.001 g, 0.005 mmol), and 0.7 mL of benzene-d6. The reaction mixture was kept at ambient temperature for 3.5 h. The reaction mixture was filtered through Celite with CH2Cl2 and concentrated in vacuo. The resultant yellow oil was purified by flash chromatography (hexanes) to afford 36 (0.022 g, 60%) as a colorless oil: 1H NMR (500 MHz, CDCl3) δ 7.29–7.34 (m, 4H), 7.13–7.15 (m, 1H), 4.33 (s, 1H), 3.48 (s, 3H), 3.31 (s, 3H), 1.10 (s, 9H), 0.91 (s, 9H); 13C NMR (125 MHz, CDCl3) δ 141.9, 128.2, 126.3, 125.6, 78.7, 58.9, 53.0, 28.6, 28.4, 22.4, 21.8; IR (thin film) 2936, 2858, 1599, 1493, 1474, 1109 cm-1; HRMS (ESI) m / z calcd for C17H30NaO2Si (M + Na)+ 317.1913, found 317.1922.

Alkyl silane 38

To a J. Young NMR tube was added propionaldehyde diethyl acetal (37) (20 μL, 0.125 mmol), silacyclopropane 10 (0.034 g, 0.150 mmol), AgO2OCF3 (0.001 g, 0.005 mmol), and 0.7 mL of benzene-d6. The reaction mixture was kept at ambient temperature for 20 min. The reaction mixture was filtered through Celite with CH2Cl2 and concentrated in vacuo. The resultant yellow oil was purified by flash chromatography (hexanes) to afford 38 (0.017 g, 50%) as a colorless oil: 1H NMR (500 MHz, CDCl3) δ 3.92–3.80 (dq, J = 9.9, 6.9, 1H and dq, J = 9.9, 6.9, 1H), 3.71 (dq, J = 8.6, 7.0, 1H), 3.32 (dq, J = 8.6, 7.0, 1H), 3.13 (dd, J = 7.5, 5.6, 1H), 1.78–1.79 (m, 2H), 1.10–1.22 (t, J = 6.9, 3H and t, J = 7.0, 3H), 1.01–1.09 (s, 9H; s, 9H; t, J = 7.4, 3H); 13C NMR (125 MHz, CDCl3) δ 75.9, 67.9, 60.1, 28.9, 28.7, 26.0, 21.9, 21.5, 18.9, 16.2, 13.8; IR (thin film) 2974, 2859, 1474, 1117, 1086, 823 cm-1; HRMS (ESI) m / z calcd for C15H34NaO2Si (M + Na)+ 297.2226, found 297.2232.

Allylic ether 39

The representative procedure for the synthesis of aryl-protected allylic alcohols was followed using 3-methyl-2-butene-1-ol (1.02 mL, 10.0 mmol), 4-(trifluoromethyl)benzyl bromide (2.27 g, 9.5 mmol), NaH (0.312 g, 13.0 mmol), and 33 mL of THF for 12 h. Purification by flash chromatography (98:2 hexanes:EtOAc) afforded 39 (2.12 g, 87%) as a colorless oil: 1H NMR (500 MHz, CDCl3) δ 7.61 (d, J = 8.5, 2H), 7.47 (d, J = 8.6, 2H), 5.39–5.42 (m, 1H), 4.55 (s, 2H), 4.02 (d, J = 6.9, 2H), 1.77 (s, 3H), 1.67 (s, 3H); 13C NMR (125 MHz, CDCl3) δ 142.8, 137.8, 129.7 (q, J = 31), 127.7, 126.5 (q, J = 293), 125.3 (q, J = 3.8), 120.7, 71.2, 67.0, 25.9, 18.1; IR (thin film) 2975, 2860, 1420, 1326, 1066, 823 cm-1; HRMS (ESI) m / z calcd for C13F3H15NaO (M + Na)+ 267.0973, found 267.0977. Anal. Calcd for C13H15OF3: C, 63.93; H, 6.19. Found: C, 63.97; H, 6.22.

Allylic silane 40

The representative procedure for the synthesis of allylic silanes was followed using allylic ether 39 (0.244 g, 1.00 mmol), silacyclopropane 10 (0.337 g, 1.50 mmol), CuOTf·PhMe (0.026 g, 0.050 mmol, 2:1 complex), and 6.7 mL of toluene for 12 h. Purification by flash chromatography (99:1 hexanes:EtOAc) afforded 40 (0.313 g, 81%) as a colorless oil: 1H NMR (500 MHz, CDCl3) δ 7.60 (d, J = 8.4, 2H), 7.46 (d, J = 8.5, 2H), 5.32–5.33 (m, 1H), 4.96 (s, 2H), 1.72 (d, J = 8.2, 2H), 1.65 (s, 3H), 1.62 (s, 3H), 1.07 (s, 18H); 13C NMR (125 MHz, CDCl3) δ 145.8, 129.2, 129.0 (q, J = 35), 125.8, 124.4 (q, J = 249), 125.1 (q, J = 3.8), 120.1, 65.5, 28.3, 25.9, 21.6, 17.7, 12.2; IR (thin film) 2933, 2859, 1325, 1127, 1067, 824 cm-1; HRMS (ESI) m / z calcd for C21F3H33NaOSi (M + Na)+ 409.2151, found 409.2155. Anal. Calcd for C21H33OSiF3: C, 65.25; H, 8.60. Found: C, 65.52; H, 8.83.

Allylic ether 41

The representative procedure for the synthesis of aryl-protected allylic alcohols was followed using 3-methyl-2-buten-1-ol (0.50 mL, 5.00 mmol), p-methoxybenzyl chloride (0.68 mL, 5.00 mmol), NaH (0.360 g, 15.0 mmol), and 17 mL of THF for 12 h. Purification by flash chromatography (95:5 hexanes:EtOAc) afforded 41 (0.990 g, 96%) as a colorless oil: 1H NMR (500 MHz, CDCl3) δ 7.28 (d, J = 8.6, 2H), 6.89 (d, J = 8.7, 2H), 5.39–5.41 (m, 1H), 4.44 (s, 2H), 3.98 (d, J = 7.0, 2H), 3.81 (s, 3H), 1.76 (s, 3H), 1.66 (s, 3H); 13C NMR (125 MHz, CDCl3) δ 159.2, 137.2, 130.7, 129.5, 121.2, 113.8, 71.8, 66.3, 55.3, 25.9, 18.1. 1H and 13C NMR spectroscopic data matched those previously reported. 28

Allylic silane 42

The representative procedure for the synthesis of allylic silanes was followed using allylic ether 41 (0.206 g, 1.00 mmol), silacyclopropane 10 (0.337 g, 1.50 mmol), CuOTf·PhMe (0.026 g, 0.050 mmol, 2:1 complex), and 6.7 mL of toluene for 12 h. Purification by flash chromatography (99:1 hexanes:EtOAc) afforded 42 (0.237 g, 68%) as a colorless oil: 1H NMR (500 MHz, CDCl3) δ 7.27 (d, J = 8.7, 2H), 6.88 (d, J = 8.7, 2H), 5.34–5.36 (m, 1H), 4.83 (s, 2H), 3.82 (s, 3H), 1.66 (d, J = 1.1, 2H), 1.62 (s, 3H), 1.55 (s, 3H), 1.05 (s, 18H); 13C NMR (125 MHz, CDCl3) δ 158.5, 134.0, 128.8, 127.1, 120.4, 113.6, 65.7, 55.3, 28.3, 25.9, 21.6, 17.7, 12.3; IR (thin film) 2933, 2859, 1325, 1127, 1067, 824 cm-1; HRMS (ESI) m / z calcd for C21H36O2SiNa (M + Na)+ 371.2382, found 371.2389.

Acknowledgments

This research was supported by the National Institute of General Medical Sciences of the National Institutes of Health (GM-54909). L.E.B. thanks the Department of Education (GAANN) for a predoctoral fellowship. K.A.W. thanks Amgen and Lilly for awards to support research. We thank Dr. Phil Dennison (UCI) for assistance with NMR spectroscopy and Dr. John Greaves and Ms. Shirin Sorooshian (UCI) for mass spectrometry.

Footnotes

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References

(1) Iwamura H, Imahashi Y. Tetrahedron Lett. 1975;16:1401–1404.
(2) Schönberg A, Praefcke K. Tetrahedron Lett. 1964;5:2043–2047.
(3) Jones M, Jr., Ando W, Kulczycki A. Tetrahedron Lett. 1967;8:1391–1396.
(4) Nozaki H, Takaya H, Moriuti S, Noyori R. Tetrahedron. 1968;24:3655–3669.
(5) Ando W, Suzuki J, Saiki Y, Migita T. J. Am. Chem. Soc. 1972;94:3870–3876.
(6) Doyle MP, Griffin JH, Chinn MS, Van Leusen D. J. Org. Chem. 1984;49:1917–1925.
(7) Friedrich K, Ulrich J, Kirmse W. Tetrahedron Lett. 1985;26:193–196.
(8) Kirmse W, Cheiem PV. Tetrahedron Lett. 1985;26:197–200.
(9) Doyle MP, Bagheri V, Claxton EE. Tetrahedron Lett. 1988;29:5119–5122.
(10) Davies HML, Clark TJ, Church LA. Tetrahedron Lett. 1989;30:5057–5060.
(11) Doyle MP, Bagheri V, Claxton EE. J. Chem. Soc., Chem. Commun. 1990:46–48.
(12) Tortorelli VJ, Jones M., Jr. J. Chem. Soc., Chem. Commun. 1980:785–786.
(13) Tzeng D, Weber WP. J. Org. Chem. 1981;46:693–696.
(14) Ishikawa M, Nakagawa K-I, Kumada M. J. Organomet. Chem. 1981;214:277–288.
(15) Ishikawa M, Katayama S, Kumada M. J. Organomet. Chem. 1983;248:251–260.
(16) Bourque LE, Cleary PA, Woerpel KA. J. Am. Chem. Soc. 2007;129:12602–12603. [PubMed]
(17) Schafer A, Weidenbruch M. J. Organomet. Chem. 1985;282:305–313.
(18) Masamune S, Murakami S, Tobita H. Organometallics. 1983;2:1464–1466.
(19) Wagner DDM, Griller D. Adv. Free Radical Chem. 1990;1:159–184.
(20) Brewster JH, Kline MW. J. Am. Chem. Soc. 1952;74:5179–5182.
(21) Heard GL, Yates BF. Aust. J. Chem. 1994;47:1685–1694.
(22) West FG, Naidu BN. J. Am. Chem. Soc. 1994;116:8420–8421.
(23) Baldwin JE, Patrick JE. J. Am. Chem. Soc. 1971;93:3556–3558.
(24) Driver TG, Woerpel KA. J. Am. Chem. Soc. 2004;126:9993–10002. [PubMed]
(25) Driver TG, Franz AK, Woerpel KA. J. Am. Chem. Soc. 2002;124:6524–6525. [PubMed]
(26) Boudjouk P, Black E, Kumarathasan R. Organometallics. 1991;10:2095–2096.
(27) Gibbons G. J. Am. Chem. Soc. 1982;104:1767–1769.
(28) Kim JD, Han G, Jeong LS, Park HJ, Zee OP, Jung YH. Tetrahedron. 2002;58:4395–4402.