Synthesis of new chiral terpyridine mono-N-oxide and di-N-oxide ligands and their applications in copper-catalyzed asymmetric cyclopropanation

New families of chiral terpyridine mono-N-oxides L-1-L-3 and di-N-oxides L-4-L-6, were synthesized in moderate to good yields by simple oxidation of their corresponding terpyridines with m-CPBA. The copper(II) triflate complexes of these ligands were found to be highly effective catalysts for asymmetric cyclopropanation of styrene with ethyl diazoacetate. The isolated yields of cyclopropane were excellent and the enantiomeric excesses of up to 83% were observed. Competition experiments with substituted styrenes showed good sigma(+) correlations with rho = -0.70 for mono-N-oxide L-3 and rho = -0.69 for di-N-oxide L-6. (C) 2002 Elsevier Science Ltd. All rights reserved.