Reaction of polyspirocyclic internal gem dibromocyclopropanes with methyllithium. An unusual carbenoid rearrangement

A skeletal rearrangement of a series of polyspiro internal gem dibromocyclopropanes in the presence of methyllithium reagents was studied. The rearranged products of two types were obtained: substituted bromocyclobutenes ( type B) and C-H insertion products ( type K) resulting from the reaction of the carbenoid intermediate H with the ether solvent. The mechanism of the carbenoid rearrangement is discussed.