THE REACTION OF 1-HALOGENO-1-LITHIOCYCLOP ROPANES WITH CUCL2 - COMPETITION BETWEEN CARBENE DIMERIZATION AND OXIDATIVE COUPLING .15.

The 1-chloro-1-lithiocyclopropanes 2a-d react at low temperature with CuCl2 to give diastereoisomeric mixtures of oxidative-coupling product s 5a-d and of 'carbene dimers' 6a-d. The relative amount of 5a-d incre ases with CuCl2 concentration and reaction time. Diastereoselectivity of the reaction seems to be low, and separation as well as spectroscop ic structure assignment of single diastereoisomers are difficult. The conformational behavior of 1,1'-dichloro-1,1'-bi(cyclopropyls) 5c and 5d is discussed. Contrary to 2a-d, 1-bromo-1-lithiocyclopropanes norma lly react with CuCl2 to give 'carbene dimers' 6 and no coupling produc ts 5. So far the only exception is 1-bromo-1-lithio-2-phenylcyclopropa ne 2e which in the presence of CuCl2 gives some percents of coupling p roducts 5e besides carbene dimers 6b as main products. An X-ray struct ure analysis of the predominant diastereoisomer 5e was performed.