Asymmetric cyclopropanation catalyzed by fluorous bis(oxazolines)-copper complexes

Fluorous bis(oxazoline)-copper(l) complexes generated in situ were tested as catalysts in the metal-catalyzed cyclopropanation of styrene with various alpha-diazoacetates. Under optimized conditions in CH2O2, quite good yields were obtained. Diastereoselectivities were found to be substrate and, to a lesser extent, ligand dependent, with trans/cis ratios ranging from 62/38 (cyclopropanation with alpha-ethyidiazoacetate 2a using ligand 1a) to 98/2 (cyclopropanation with methyl pheny1diazoacetate 2c using ligand 1b). Enantioselectivities up to 84% ee for the trans-isomer and 81% ee for the cis-isomer were observed using ligand 1b. Fluorous bis(oxazoline)-copper(l) complexes could be very easily separated from the products by simple precipitation using hexane, and recycled without loss of stereo- as well as enantioselectivities. (c) 2006 Published by Elsevier Ltd.