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

Fluorous bis(oxazoline)–copper(I) complexes generated in situ were tested as catalysts in the metal-catalyzed cyclopropanation of styrene with various α-diazoacetates. Under optimized conditions in CH2Cl2, 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 α-ethyldiazoacetate 2a using ligand 1a) to 98/2 (cyclopropanation with methyl phenyldiazoacetate 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(I) complexes could be very easily separated from the products by simple precipitation using hexane, and recycled without loss of stereo- as well as enantioselectivities.

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12,12-Bis[(4S)-4-tert-butyl-1,3-oxazolin-2-yl](9H,9H,10H,10H,11H,11H,13H,13H,14H,14H,15H,15H)perfluorotricosaneC37H38F34N2O2[α]D25=-24(c1,CHCl3)Source of chirality: commercially availableAbsolute configuration: S,S