Binuclear versus mononuclear copper complexes as catalysts for asymmetric cyclopropanation of styrene

A number of (S)-(-)-2-amino-1,1-diaryl-1-propanol compounds have been synth esized. They were used to form the binuclear copper complexes through a spo ntaneous assembly of the individual components, the beta-aminoalcohol, 2-hy droxy-5-methyl-1,3-benzenedialdehyde, and copper acetate monohydrate, in me thanol. These binuclear complexes were examined as asymmetric catalysts for cyclopropanation of styrene by ethyl diazoacetate. Moderate improvement in enantioselectivity has been observed for the binuclear versus mononuclear copper complexes. The e.e. values up to 87% for trans and 93% for cis produ cts and the ratio between trans and cis products up to 9:1 have been obtain ed. (C) 1999 Elsevier Science Ltd. All rights reserved.