Reduction of aryltrimethylsilanes as a synthetic method. Part I. Electrochemical reduction

Abstract

Electrochemical reduction of aryltrimethyl-silanes and -germanes affords a convenient preparative route to silyl- and germyl-substituted cyclohexa-1,4-dienes, since in most cases the products resist further reduction. The nature of the products is in accord with a Birch-type reduction mechanism. Trimethyl(phenyl)silane gives cyclohexa-2,5-dienyltrimethylsilane in 79% yield. The three bis(trimethylsilyl)benzene isomers and trimethyl-m-tolylsilane give the isomers predicted on the basis of the electronic effects of the substituent groups, but trimethyl-p-tolylsilane, in which the directing effects conflict, gives a mixture of products. Steric as well as electronic influences are probably important. Trialkyl(phenyl)germanes behave analogously to trimethyl(phenyl)silane, but trimethyl(phenyl)tin undergoes cleavage of the tin–carbon bond. The two stereoisomers of 3,6-bis(trimethylsilyl)cyclohexa-1,4-diene were isolated and tentatively assigned configurations.