Kupfer(II)‐chlorid‐katalysierte ‘Carben‐Dimerisierung’ von 1‐Halogeno‐1‐Lithiocyclopropanen: Ein einfacher Zugang zu Bi(cyclopropylidenen)

Abstract

Copper(II)‐Chloride Catalyzed ‘Carbene Dimerization’ of 1‐Halogeno‐1‐lithiocyclopropanes: A Simple Access to Bi(cyclopropylidenes) 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°, to give 1‐bromo‐1‐lithiocyclopropanes 2a – n , followed by treatment with CuCl 2 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 diastereoisomer of 11k ( Fig. 1 ).