An unexpected aminocyclopropane reductive rearrangement

A reductive rearrangement of aminocyclopropanes is described for the synthesis of cis- or trans-fused bicyclic 1,2-diaminocyclobutanes. Ionization of a cyclic aminal using BF3·OEt2 induces rearrangement to a cyclobutyl iminium ion, which is subsequently reduced by Et3SiH. Substitution with allyltrimethylsilane allows carbon incorporation, giving a quaternary center. Silyloxy-substituted cyclopropanes rearrange rapidly to cyclobutanones which react with NaBH4 to provide 1,2-aminohydroxycyclobutanes. These aminals were generated by the reduction of a Boc-imide with DIBAL-H or LiBH4.