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Synlett 2002(4): 0553-0556
DOI: 10.1055/s-2002-22709
LETTER
© Georg Thieme Verlag Stuttgart · New York

Compared Behaviors of trans- and cis-α,β-Epoxy-γ,δ-vinyl-silanes Towards Nucleophiles and Bases: High Regioselective Ring Opening and Deprotonation

Jean-Charles Marié, Christine Courillon, Max Malacria*
Université P. et M. Curie, Laboratoire de Chimie Organique de Synthèse, associé au CNRS Tour 44-54, B. 229, 04 place Jussieu, 75252 PARIS Cedex 05, France
e-Mail: malacria@ccr.jussieu.fr;
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Publikationsverlauf

Received 18 January 2002
Publikationsdatum:
05. Februar 2007 (online)

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Abstract

This work describes the regioselective nucleophilic ring opening and the deprotonation of α,β-epoxy-γ,δ-vinyl-silanes with nitrogen, sulfur and carbon nucleophiles. In an original way, our results point out the α,β-epoxy-silane-like or vinyloxirane-like behavior of α,β-epoxy-γ,δ-vinyl-silanes according to their configuration and to the type of the nucleophile. Furthermore we report an easy stereoselective access to α-alkylated-α"-silylated-β,γ-unsaturated-ketones.

Key words

α,β-epoxy-γ,δ-vinyl-silanes - ring opening of oxiranes - regioselectivity.

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Preparation of 7a: To a solution of the trans-silylated vinyloxirane 1a (100 mg, 0.54 mmol, 1 equiv) in pentane (10 mL), under argon, was added dropwise, at -30 °C, to a solution of tert-butyllithium in pentane (0.72 mL of a 1.5 M, 1.08 mmol, 2 equiv). The reaction was monitored by TLC and after completion of the reaction it was quenched at this temperature, with a 1:1 solution of propionic acid:diethyl ether. The reaction mixture was then allowed to warm to room temperature and treated with an excess of a saturated sodium hydrogenocarbonate solution. The aqueous layer was then extracted with ethyl acetate. The combined organic layers were washed with brine and dried over anhydrous sodium sulfate. Flash chromatography on silica gel (petoleum ether/diethyl ether, 98:2) gave 116 mg (89%) of the desired product as a 2:1 mixture of two diastereomers E/Z.
E diastereomer: 1H NMR (200 MHz, C6D6): δ = 5.59 (1 H, dd, J = 15.25, 5.40 Hz), 5.44 (1 H, dt, J = 15.25, 6.90 Hz), 3.93 (1 H, d, J = 5.90 Hz), 1.90 (2 H, d, J = 6.40 Hz), 1.03 (9 H, s), 0.89 (9 H, s), 0.09 (3H, s), -0.02 (3H, s).
13C NMR (50 MHz, C6D6): δ = 136.33, 124.80, 67.77, 48.42, 30.41 (3 C), 28.23 (3 C), 19.44, 18.16, -6.18, -7.82.
Z diastereomer: 1H NMR (200 MHz, C6D6): δ = 5.64 (1 H, dd, J = 10.82, 10.34 Hz), 5.34 (1 H, m), 4.40 (1 H, d, J = 10.37 Hz), 2.01 (1 H, d, J = 9.20 Hz), 1.80 (1 H, dd, J = 5.62, 1.70 Hz) 1.05 (9 H, s), 0.86 (9 H, s), 0.13 (3 H, s), 0.00 (3 H, s).
13C NMR (50 MHz, C6D6): δ = 133.62, 125.95, 62.38, 41.89, 29.50 (3 C), 27.46 (3 C), 19.60, 17.49, -7.07, -8.26.

28

Preparation of 10 (typical procedure for lithiation of the cis-epoxide): To a cold solution (-116 °C) of the cis-silylated vinyloxirane 1b (200 mg, 1.08 mmol, 1 equiv) and TMEDA (0.25 mL, 1.63 mmol, 1.5 equiv) in diethyl ether (10 mL) was added dropwise a solution of sec-butyllithium in cyclohexane (1.67 mL of a 1.3 M, 2.17 mmol, 2 equiv). The reaction mixture was stirred under argon at this temperature until the bright yellow lithiated anion precipitated (ca 30-45 minutes). Methyliodide (0.68 mL, 10.85 mmol, 10 equiv) was then quickly added to the solution and after 10 minutes at -116 °C, the mixture was allowed to warm to room temperature. The organic layer was washed with a saturated ammonium chloride solution, and the aqueous phase was extracted with diethyl ether. The combined organic layers were washed with brine and dried over anhydrous sodium sulfate. Evaporation under reduced pressure afforded the crude product that was purified by flash chromatography on silica gel (petroleum ether/diethyl ether, 99:1). The desired product was obtained in 89% yield.
1H NMR (200 MHz, C6D6): δ = 5.74 (1 H, ddd, J = 17.70, 10.32, 8.36 Hz), 5.25 (1 H, dd, J = 17.22, 1.48 Hz), 5.04 (1 H, dd, J = 10.82, 0.98 Hz), 3.01 (1 H, d, J = 8.38 Hz), 1.18 (3 H, s), 0.90 (9 H, s), 0.05 (3 H, s), 0.00 (3 H, s).
13C NMR (50 MHz, C6D6): δ = 138.09, 119.95, 67.01, 56.64, 28.53 (3 C), 25.87, 18.28, -3.85, -4.21.

29

Rearrangement of 10 with palladium(0): Triphenylphosphite (26 µL, 0.10 mmol, 0.2 equiv) was added via a syringe to a stirred solution of palladium diacetate (6 mg, 0.03 mmol, 0.05 equiv) in freshly distilled THF (1 mL). After 10 minutes at room temperature, a solution of vinylepoxysilane 10 (100 mg, 0.5 mmol, 1 equiv) in THF (2 mL) was transferred by cannula into the pale yellow reaction mixture. After completion of the rearrangement (ca 2 h), the crude mixture was filtered through a pad of celite and the organic layer was directly evaporated under reduced pressure. After purification by flash chromatography on silica gel, the ketone 14 was obtained in 82% yield.
1H NMR (200 MHz, CDCl3): δ = 6.06 (1 H, ddd, J = 17.22, 10.82, 10.32 Hz), 4.93 (1 H, dd, J = 10.34, 1.48 Hz), 4.90 (1 H, dd, J = 16.74, 1.48 Hz), 3.41 (1 H, d, J = 10.82 Hz), 2.11 (3 H, s), 0.91 (9 H, s), 0.07 (3H, s), 0.03 (3H, s).
13C NMR (50 MHz, C6D6): δ = 207.42, 134.36, 113.99, 54.01, 31.30, 26.84 (3 C), 18.38, -6.12, -6.63.