New Bi(cyclopropylidenes) by CuCl2-Induced ‘Carbene Dimerization’ of 1-Bromo-1-lithiocycIopropanes

A series of so far unknown bi(cyclopropylidenes) 5 are prepared in a simple one-pot reaction by halogenolithio exchange between 1,1-dibromocyclopropanes 1ac as well as 1ei and BuLi at −95°, to give 1-bromo-1-lithiocyclopropanes 2ac as well as 2ei, followed by treatment with CuCl2 at low temperature and a simple workup at room temperature (Table 1). The influence of reaction parameters on yields of 5 (Tables 2, 4, and 5) and diastereoselectivity of the reaction 2 [RIGHTWARDS ARROW] 5 (Table 3) are discussed. In view of an elucidation of the reaction mechanism, first kinetic experiments of the quantitative reaction 1c [RIGHTWARDS ARROW] 2c [RIGHTWARDS ARROW] 5c are reported.