Enantioselective catalytic cyclopropanation of styrenes by copper complexes with chiral pinene-[5,6]-bipyridine ligands

Substituted mono- and bis-pinene-[5,6]-bipyridines are useful ligands in asymmetric copper-catalyzed cyclopropanation by styrenes. Copper complexes were prepared either in situ or prior to the reaction. The catalytic reaction of styrene with ethyl diazoacetate and Cu-11b yields ethyl trans-phenylcyclopropane carboxylate in >99% yield and 87% e.e. at 0 degreesC. The corresponding cis-configured cyclopropane was produced with an e.e. of 90%. The cis/trans ratio is 22:78. Other ligands of this series are less effective, Various olefins were tested as substrates but exo-methylene olefins show the best results. (C) 2000 Elsevier Science Ltd. All rights reserved.