Synthesis, stereochemistry, and reactions of 2,5-diphenylsilacyclopentenes

1,1-Disubstituted derivatives of 2,5-diphenylsilacyclopent-3-enes, namely those having the 1,1-diphenyl, 1,1-dimethyl, 1-alkoxy-1-methyl and 1,1-dialkoxy, were prepared by a one-pot reaction of (1E, 3E)-1,4-diphenyl-1,3-butadiene and dichlorosilanes in the presence of magnesium. Each silacyclopentene was formed as a mixture of one trans and two cis isomers. 1-Ethoxy-1-methyl-2,5-diphenylsilacyclopent-3-ene and 1,1-diethoxy-2,5-diphenylsilacyclopent-3-ene were reacted with optically active alcohols to furnish the corresponding diastereomers. The absolute configuration of one of these diastereomers was determined by X-ray structure analysis. The mixture of cis and trans diastereomers was lithiated by lithium diisopropylamide (LDA) to obtain the trans forms selectively, with the stereoselectivity being determined by NOE experiments.