Kupfer(II)-chlorid-katalysierte 'Carben-Dimerisierung' von 1-Halogeno-1-lithiocyclopropanen: Ein einfacher Zugang zu Bi(cyclopropylidenen)

Article abstract of DOI:10.1002/hlca.19950780509

A series of 13 bi(cyclopropylidenes) 11 are prepared in a simple one-pot reaction by halogeno-lithio exchange between 1,1-dibromocyclopropanes 1a-n and BuLi, in most cases at -95 deg C, to give 1-bromo-1-lithiocyclopropanes 2a-n, followed by treatment with CuCl2 at low temperature and a simple workup at room temperature (Scheme 3c and Table 1).The yields of bi(cyclopropylidenes) 11 strongly depend on reaction parameters, as explicitly shown for the conversion 1f->-> 11f (Tables 2-8).Mixed couplings between two different carbenoids are possible (Scheme 4), while diastereoselectivity of the active transition-metal complex seems to be low.The structures of bi(cyclopropylidenes) 11 are confirmed by spectroscopic data as well as by X-ray analysis of an isolated crystalline diastereomer of 11k (Fig. 1).