Synthesis of Functionalized Allylsilanes via the Condensation of α,β-Unsaturated Carbonyl Compounds with γ-Trimethylsilylmethylallylzircocene Followed by Anionic Oxy-Cope Rearrangement

Abstract

Condensation of α,β-unsaturated carbonyl compounds with γ-trimethylsilylmethylallylzircocene followed by anionic oxy-Cope rearrangement provided a novel method for the synthesis of functionalized allylsilanes compounds possessing a carbonyl group in the same molecule, which are versatile intermediates for intramolecular allylsilylation, giving cyclopentanols on treatment with n-Bu₄NF.

Key words

allylzirconcene - oxy-Cope rearrangement - allylsiliane - cyclopentanol

References

• 1 Hill RK. In Comprehensive Organic Synthesis   Trost BM. Fleming I. Pergamon; Oxford: 1991.  Chap. 7.1.
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• 3 Paquette LA. Synlett  1990,  67 
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• 7b Chino M. Matsumoto T. Suzuki K. Synlett  1994,  359 
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8

General Procedure for Preparation of 4-Trimethyl-silylmethyl-1,5-dien-3-ols: Under a N₂ atmosphere at -78 °C, to a stirred suspension of Cp₂Zr(H)Cl (2 mmol) in CH₂Cl₂(5 mL) was added allene 1 (3 mmol) in CH₂Cl₂ (3 mL). The reaction was gradually warmed up to r.t., resulting in a red solution. The reaction was re-chilled to -78 °C (or 0 °C), to which a solution of aldehyde (or ketone) (1 mmol) in CH₂Cl₂(5 mL) was added. After 30 min, the reaction was quenched by adding sat. aq NaHCO₃. Extractive workup followed by purification (SiO₂ preparative TLC, hexane) gave 4 and 5. Selected Data of 4e: IR(neat): 1930, 11875, 1600, 1490, 1450, 1410, 1375, 1325, 1175, 1060, 853 cm^-1. ¹H NMR (400 MHz, CDCl₃): δ = 6.54 (d, J = 8.0Hz, 1 H), 6.34 (d, J = 8.0 Hz, 1 H), 5.56 (ddd, J = 16.4, 10.8, 9.6 Hz, 1 H), 5.19 (d, J = 10.8 Hz, 1 H), 5.17 (d, J = 16.4 Hz, 1 H), 2.28(m, 1 H), 2.2.02 (br s, 2 H), 1.54 (m, 1 H), 1.35 (s, 3 H), 0.98 (m, 1 H), 0.63 (m, 1 H), 0.08 (s, 9 H). ¹³C NMR (100 MHz, CDCl₃): δ = 140.7, 136.5, 136.2, 132.0, 128.4, 127.4, 121.4 118.6, 75.4 52.3, 26.3, 17.4, 0.35. MS (EI): m/z (%) = 354 (2.86), 105(100). Anal. Calcd for C₁₇H₂₅BrOSi: C, 57.78; H, 7.13. Found: C, 58.04; H, 7.26.

10

General Procedure for Preparation of 7:
KH (30% dispersion in mineral oil, 5 mmol) was washed with anhyd hexanes and suspended in THF (8 mL) to which I₂ (0.15 mmol) and 4-trimethylsilylmethyl-1,5-dien-3-ol (1 mmol) were added and the mixture was stirred at r.t. for 7 h. Upon cooling to 0 °C, the reaction mixture was quenched by adding 10% aq NH₄Cl solution and the aq layer extracted with Et₂O (3 × 10 mL). The combined organic layers were washed with sat. NaCl, dried over anhyd MgSO₄, filtered and concentrated. Purification by flash chromatography (hexane-EtOAc = 15:1) gave allylsilane.
Selected Data of 7c: IR(neat): 1690, 1665, 1611, 1590, 1565, 1485, 860, 750, 695 cm^-1. ¹H NMR (400 MHz, CDCl₃): δ = 7.08-7.12 (m, 4 H), 5.38 (dt, J = 16.0, 8.0 Hz, 1 H), 5.10 (dt, J = 16.0, 6.4 Hz, 1 H), 3.16 (m, 1 H), 2.72 (m, 2 H), 2.32 (s, 3 H), 2.28 (m, 2 H), 2.02 (s, 3 H), 1.37 (d, J = 8.0 Hz, 2 H), -0.06 (s, 9 H). ¹³C NMR (100 MHz, CDCl₃): δ = 207.7, 144.5, 131.0, 128.9, 127.8, 127.6, 126.9, 51.3, 41.4, 31.8, 24.9, 21.4, -1.59. MS (EI): m/z (%) = 289 (2.12), 73(100). Anal. Calcd for C₁₈H₂₈OSi: C, 74.94; H, 9.78. Found: C, 75.11; H, 10.04.

12

General Procedure for Preparation of 10:
To a solution of allylsilane (1mmol) in THF (8 mL) was added n-Bu₄NF (2 mmol) and the mixture was stirred at r.t. for 2 h. The reaction mixture was quenched with 10% aq NH₄Cl solution and the aq layer was extracted with Et₂O (3 × 10 mL). The combined organic layers were washed with water and sat. NaCl, dried over anhyd MgSO₄, filtered and concentrated. Purification by flash chromatography (hexane-EtOAc = 10:1) gave 10. Selected Data of 10b: ¹H NMR (400 MHz, CDCl₃): δ = 7.20-7.38 (m, 5 H), 5.87 (ddd, J = 8.4, 10.0, 17.2 Hz, 1 H), 5.14 (d, J = 17.2 Hz, 1 H), 5.12 (d, J = 10.0 Hz, 1 H), 348 (m, 1 H), 2.72 (m, 1 H), 2.31 (m, 1 H), 2.08 (br s, 1 H), 1.88 (m, 1 H), 1.70 (m, 1 H), 1.33 (s, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 145.4, 139.2, 128.8, 127.4, 126.5, 115.9, 81.3, 56.9, 49.7, 42.3, 40.1, 26.8. MS (EI): m/z (%) = 202(5.7). Anal. Calcd for C₁₄H₁₈O: C, 83.12; H, 8.97. Found: C, 83.43; H, 9.06.