The mechanism of [2 + 1] and [2 + 2] cycloaddition reactions of 1-phenylseleno-2-(trimethylsilyl)ethene: an isotopic labelling study

Abstract

The reactions of deuterio-labelled 1-seleno-2-silylethenes with trimethyl 2-phosphonoacrylate 2 and methyl vinyl ketone 4 in the presence of SnCl₄ gave deuterio-substituted cyclopropanes with 1,2-silicon migration. The reaction of deuterio-labelled 1-seleno-2-silylethenes with dimethyl 2,2-dicyanoethene-1,1-dicarboxylate 6 in the presence of SnCl₄ and ZnBr₂ gave deuterium-substituted cyclobutanes without silicon migration. This labelling study strongly confirms the 1,2-silicon migration for [2 + 1] cycloadditions of 1 and non-1,2-silicon migration for the [2 + 2] cycloaddition reactions, respectively.