Carbenoid rearrangement in the series of substituted gem-dibromospiropentanes

A series of new substituted gem-dibromospiropentanes was studied in a reaction with methyllithium at -55...-50 degrees C. This reaction is a carbenoid rearrangement that leads to the formation of monomeric and dimeric bromocyclobutenes and also to the products of cyclobutylidene insertion into a C-H bond of the solvent depending on the character of substituents in the dibromospiropentane fragment.