A facile formal [2+1] cycloaddition of styrenes with alpha-bromocarbonyls catalyzed by copper: efficient synthesis of donor-acceptor cyclopropanes

Reactions of 2-bromoesters and styrenes underwent a [2+1] cyclo-addition reaction, i.e., cyclopropanation, to produce donor-acceptor (D-A) cyclopropanes through a radical addition-ring closure process. In this reaction, the combination of copper(II) complex and amines is found to be a good catalyst system to obtain cyclic compounds in high yields. This reaction provides an efficient protocol to synthesize D-A cyclopropanes, which are very important building blocks in organic synthesis.