Stereoselective TiCl4-mediated aldol reactions starting from acylsilanes.
Abstract
A simple and efficient method for the prepn. of β-hydroxyacylsilanes has been developed through a TiCl4-mediated aldol reaction of acylsilanes with aldehydes. Acylsilane EtCOSiMe2Ph reacted with PhCHO giving 80:20 diastereomeric syn-anti mixt. of PhCH(OH)CHMeCOSiMe2Ph under TiCl4 catalysis. Similarly, arom. aldehydes contg. electron-withdrawing substituents, and isobutyraldehyde iPrCHO gave the hydroxyacyl silanes RCH(OH)CHMeCOSiMe2Ph with reasonable yields and high syn-selectivity. A selection of Lewis acids has been assessed, and other parameters such as solvent and temp. have been optimized. These aldol reactions occur under mild conditions and furnish a selection of β-hydroxy acylsilanes in fair-to-good yields with high syn selectivities (up to 99 %).