Synthesis of Silyl Enol Ethers and Their Aldol Reaction Utilizing 2, 5-Dimethyl-1-silacyclopentane and 2, 5-Diphenyl-1-sila-3-cyclopentene derivatives

摘要

Silyl enol ethers were prepared by the reaction of ketones with r-1, t-2, t-5-and r-1, t-2, c-5-isomeric mixture of 1-chloro-2, 5-dimethyl-1-phenyl-1-silacyclopentane and 1-alkyl-1-chloro-2, 5-diphenyl-1-sila-3-cyclopentene, and their aldol reaction was investigated. The silyl enol ethers were prepared in the presence of triethylamine as base in N, N-dimethylformamide (DMF) or LDA as base in THF. The isomer ratio of the silyl enol ethers implied that retention occurred on Si-substitution in the presence of triethylamie and some inversion occurred on Si-substitution in LDA. The aldol reaction of these silyl enol ethers were investigated y a reaction with benzaldehyde in the presence of titanium tetrachloride. Teh aldol products were separated by a column chromatography using silica gel, and obtained as the diastereomers of (R~*, R~*) and (R~*, S~*) forms. The silyl enol ethers from 1-chloro-2, 5-dimethyl-1-phneyl-1-silacyclopentane gave more (R~*, R~*) form, and the enol ethers from 1-alkyl-1-chloro-2, 5-diphenyl-1-sila-3-cyclopentene gave (R~*, R~*) form selectively.