Stereospecific and regioselective isocyanide insertions into siliranes and reactions of the resulting iminosilacyclobutanes

The insertions of p-tolyl and tert-butyl isocyanide into siliranes yielded iminosilacyclobutanes with stereospecific retention of configuration. Monosubstituted siliranes underwent insertion into the more substituted Si-C bond of the ring, although this regioselectivity was eroded as substitution increased on the silirane ring. The iminosilacyclobutane products tautomerized thermally or in the presence of a palladium catalyst to yield the thermodynamically more stable aminosilacyclobutenes. Ring-expansion reactions of iminosilacyclobutanes were promoted by acids: treatment with aqueous copper sulfate produced an oxasilacyclopentane in high yield, whereas with trifluoroacetic acid, oxasilacyclohexanes were formed.