OBSERVATIONS RELATING TO THE MODE OF FORMATION OF CYCLOPROPYLIDENE DIMERS IN THE REACTION OF GEM-DIBROMOCYCLOPROPANES WITH METHYLLITHIUM

Treatment of the gem-dibromocyclopropane (5) with methyllithium in diethyl ether at –80°C gives not only the syn- and anti-cyclopropylidene dimers (12) and (13), respectively, but the related species (14) and (15) as well. The isolation of this latter pair of products lends weight to the argument that β-halobicyclopropylyllithium compounds such as (18) are the immediate precursors to the cyclopropylidene dimers.