Chiral copper(II)-Schiff base complexes as catalysts for asymmetric cyclopropanation of styrene

Twelve chiral copper (II)-Schiff base complexes, derived from (R)-(+)-2-amino-1,1-diaryl-1-propanol with substituted salicylaldehydes, were examined as a catalyst for asymmetric cyclopropanation of styrene with ethyl diazoacetate. It was found that the substituents at 3- and 5- positions of salicylaldehyde in the ligands had great effects on catalytic activity and enantioselectivity of the catalyst. The complex with strong electron-withdrawing group (NO2) at 5-position and the smallest stereo-hinder (H) at 3-position of salicytaidehyde showed highly catalytic activity and enantioselectivity, up to ee = 87.4% for trans and ee 82.8% for cis isomers respectively, and the ratio 39/61 of cis to trans isomers was obtained at 40 degreesC with 1,2-dichloroethane as solvent