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Regioselective Hydrosilylations of Propiolate Esters With Tris(trimethylsilyl)silane

Regioselective Hydrosilylations of Propiolate Esters With Tris(trimethylsilyl)silane

Yang Liu, Shoko Yamazaki, Shinichi Yamabe

J Org Chem. 2005 Jan 21;70(2):556-61.

PMID: 15651801

Abstract:

Lewis acid and substituent dependency on the regioselectivity of hydrosilylation of propiolate esters 1a-c with tris(trimethylsilyl)silane (2a) was found. The reaction of methyl and ethyl propiolate esters and 2a without Lewis acid and in the presence of EtAlCl2 and Et2AlCl gave beta-silicon-substituted Z-alkenes 3 selectively. On the other hand, reaction in the presence of AlCl3 in dichloromethane gave alpha-silicon-substituted alkenes 4. In the case of trifluoroethyl propiolate ester 1c, reaction with aluminum chloride-based Lewis acids gave alpha-silicon-substituted alkenes 4 exclusively. Two competitive mechanisms, free-radical and ionic, are proposed as the source of the complementary regioselectivity displayed in these reactions. A transition state of the radical-forming step was obtained computationally. The reaction of various reactive acetylene substrates and 2a without Lewis acid and without solvent at room temperature gave beta-silicon-substituted Z-alkenes 3 selectively.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP1873774	Tris(trimethylsilyl)silane		1873-77-4	Price

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