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

Yukinori NAGAO*, Nobuki TANAKA, Nobuo NAMIKI and Kouzo KOZAWA

Department of Industrial Chemistry, Faculty of Science and Technology, Science University of Tokyo; Noda-shi 278-8510 Japan

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 triethylamine and some inversion occurred on Si-substitution in LDA.
The aldol reaction of these silyl enol ethers were investigated by a reaction with benzaldehyde in the presence of titanium tetrachloride. The 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-phenyl-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.

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