Enantioselective catalytic cyclopropanation of styrenes by copper complexes with chiral pinene-[5,6]-bipyridine ligands
摘要:
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.
Re(I) tricarbonyl bipyridine and terpyridine complexes catalyse stereospecific cyclopropanation of alkenes; high selectivity of cyclopropane vs coupling and an ee of 73% and 62% for cis- and trans-cyclopropanes of styrene respectively were achieved with the [Re(L)(CO)(3)(MeCN)]OTf complex (L = chiral C(2)-symmetric terpyridine ligand).
Enantioselective catalytic cyclopropanation of styrenes by copper complexes with chiral pinene-[5,6]-bipyridine ligands
作者:Didier Lötscher、Stefan Rupprecht、Helen Stoeckli-Evans、Alex von Zelewsky
DOI:10.1016/s0957-4166(00)00401-8
日期:2000.11
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.