Indium-Silicon Combined Lewis Acid Catalyst for Direct Allylation of Alcohols with Allyltrimethylsilane in Non-Halogenated Solvent

Abstract

A direct allylation of alcohols is effectively catalyzed by a combined Lewis acid system of InCl₃ and Me₃SiBr. This system allows use of non-halogenated solvents such as hexane and application to a wide range of alcohols.

Key words

indium - alcohols - direct allylation - Lewis acid - silicon

References

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• 8 In the allylation of 1-phenylethanol (1a) using B(C₆F₅)₃, elimination of alcohol 1a to form styrene could readily occur (see ref. 3). Only a dimeric ether was obtained by InBr₃, see: Kim SH. Shin C. Pae AN. Koh HY. Chang MH. Chung BY. Cho YS. Synthesis  2004,  1581 
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• 10 The allylation of alcohol in the presence of Yb(OTf)₃ was not promoted at all, although the enhancement of the Lewis acidity using the combination of Yb(OTf)₃ and Me₃SiCl was reported, see: Yamanaka M. Nishida A. Nakagawa M. Org. Lett.  2000,  2:  159 
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4

Non-halogenated solvents such as hexane, THF and DMF provided less satisfactory results in the allylation of benzhydrol (1b, see ref. 3).

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General Methods.
IR spectra were recorded as thin films on a HORIBA FT-720 spectrophotometer. ¹H NMR and ¹³C NMR spectra were obtained with TMS as internal standard. Mass spectra were recorded on a JEOL JMS-DS303. MALDI-TOF MS was measured on an Applied Biosystem Voyager RP using dithranol matrix. Column chromatography was performed on silica gel (Merck C60). Bulb-to-bulb distillation (Kugelrohr) was accomplished in a Sibata GTO-250RS at the oven temperature and pressure indicated. Yields were determined by ¹H NMR using internal standards.
Typical Procedure for Allylation of 1a (Table 2, Entry 1).
To a mixture of InCl₃ (0.05 mmol) and 1-phenylethanol (1a, 1.0 mmol) in hexane (1 mL) was added allyltrimethylsilane (2, 2.0 mmol) and Me₃SiBr (0.1 mmol) under nitrogen. The reaction mixture was stirred under the reaction conditions noted in the text. The resulting mixture was poured into Et₂O (50 mL) and aq NaHCO₃ (30 mL). The solution was extracted with Et₂O and the organic layer was dried over MgSO₄. The evaporation of the ether solution gave the crude product, which was analyzed by NMR.
Typical Procedure for Allylation by Slow Addition of 1a (Table 2, Entry 2).
To a mixture of InCl₃ (0.05 mmol), Me₃SiBr (0.1 mmol) and allyltrimethylsilane (2, 3.0 mmol) in hexane (1 mL) was slowly added a solution of 1-phenylethanol (1a, 1.0 mmol) in hexane (1 mL) for 10 min at 50 °C under nitrogen. The reaction mixture was stirred for 110 min. The resulting mix-ture was poured into Et₂O (50 mL) and aq NaHCO₃ (30 mL). The solution was extracted with Et₂O and the organic layer was dried over MgSO₄. The evaporation of the ether solution gave the crude product, which was analyzed by NMR.
Product Data.
All products 3a-f are known compounds. The products
3a-c showed spectra in an excellent agreement with our previous reported data. [3] The spectral data of 3d was in an excellent agreement with the sample which is commercially available. Our spectral data of 3e [14] and 3f [15] are shown below.
4-Ferrocenyl-1-pentene ( 3e): according to the typical procedure, this compound was prepared from 1e, 2, InCl₃ and Me₃SiBr to give the product as a brown liquid after chromatography(hexane). Further purification was performed by distillation under reduced pressure; bp 95 °C/0.1 mmHg. IR:(neat): 1639 (C=C) cm^-1. ¹H NMR (400 MHz, CDCl₃): δ = 5.78 (dddd, J = 17.9, 10.4, 7.7, 6.5 Hz, 1 H, 2-H), 5.00 (ddt, J = 17.9, 1.2, 1.2 Hz, 1 H, 1-H^A), 4.99 (ddt, J = 10.4, 1.2, 1.2 Hz, 1 H, 1-H^B), 4.12-4.11 (m, 5 H, C₅H₅), 4.06 (s, 4 H, C₅H₄), 2.55 (ddq, J = 8.7, 5.1, 6.8 Hz, 1 H, 4-H), 2.36 (dddt, J = 13.8, 6.5, 5.1, 1.2 Hz, 1 H, 3-H^A), 2.07 (dddt, J = 13.8, 8.7, 7.7, 1.2 Hz, 1 H, 3-H^B), 1.21 (d, J = 6.8 Hz, 3 H, 5-H₃). ¹³C NMR (100 MHz, CDCl₃): δ = 137.38 (d, C-2), 115.71 (t, C-1), 95.33 (s, ipso-carbon in C₅H₄), 68.35 (d, C₅H₅), 66.96 (d), 66.92 (d), 66.80 (d), 65.93 (d), 43.08 (t, C-3), 32.94 (d, C-4), 20.01 (q, C-5). MS (EI, 70 eV): m/z (%) = 254 (58)[M⁺], 213 (100) [M⁺ - CH₂CH=CH₂], 121 (23) [M⁺ - C₅H₄CH(CH₃)CH₂CH=CH₂]. HRMS (EI, 70 eV): m/z calcd for C₁₅H₁₈Fe: 254.0758 [M⁺]; found: 254.0752. Anal. Calcd for C₁₅H₁₈Fe: C, 70.89; H, 7.14. Found: C, 70.60; H, 7.09.
3-Allylcyclohexene ( 3f): according to the typical procedure, this compound was prepared from 1f, 2, InCl₃ and Me₃SiBr to give the product as a colorless liquid after distillation under reduced pressure; bp 110 °C/100 mmHg. IR:(neat): 1643 (C=C) cm^-1. ¹H NMR (400 MHz, CDCl₃): δ = 5.81 (ddt, J = 16.9, 10.1, 7.0 Hz, 1 H, 3-CH₂CH=CH₂), 5.68 (ddd, J = 10.1, 5.8, 3.6 Hz, 1 H, 1-H), 5.59 (dd, J = 10.1, 2.1 Hz, 1 H, 2-H), 5.05-4.99 (m, 2 H, 3-CH₂CH=CH ₂), 2.17-2.12 (m, 1 H, 3-H), 2.06 (ddd, J = 13.0, 6.3, 6.3 Hz, 2 H, 3-CH ^AH^BCH=CH₂), 2.05 (ddd, J = 13.0, 6.3, 6.3 Hz, 2 H, 3-CH^A H ^BCH=CH₂), 2.00-1.94 (m, 2 H, 6-H₂), 1.80-1.68 (m, 2 H, 4-H^A and 5-H^A), 1.58-1.47 (m, 1 H, 5-H^B), 1.28-1.18 (m, 1 H, 4-H^B). ¹³C NMR (100 MHz, CDCl₃): δ = 137.25 (d, 3-CH₂ CH=CH₂), 131.39 (d, C-2), 127.2 (d, C-1), 115.71 (t, 3-CH₂CH=CH₂), 40.65 (t, 3-CH₂CH=CH₂), 35.01 (d, C-3), 28.80 (t, C-4), 25.27 (t, C-6), 21.41 (t, C-5). MS (EI, 70 eV): m/z (%) = 122 (6) [M⁺], 81 (100) [M⁺ - CH₂CH=CH₂], 79 (22). HRMS (EI, 70 eV): m/z calcd for C₉H₁₄: 122.1096 [M⁺]; found: 122.1091.

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Elimination of alcohols 1e occurred in the presence of combined Lewis acid in hexane to give polyvinylferrocene rather than the desired product. Polyvinylferrocene was identified by MALDI-TOF MS analysis.

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Large-Scale Synthesis of 3a.
To a mixture of InCl₃ (5 mmol), Me₃SiBr (10 mmol) and allyltrimethylsilane 2 (300 mmol) in hexane (100 mL) was slowly added a solution of 1a (100 mmol) in hexane (100 mL) for 1 h under nitrogen at 50 °C. After further stirring for 1 h at 50 °C, aq NaHCO₃ (100 mL) was added to the reaction mixture. The mixture was extracted with Et₂O and the organic layer was dried over MgSO₄. The evaporation of the ether solution followed by the distillation (34 °C/1.5 mmHg) gave the allylated product 3a in 84% yield (12.3g).