First enantioselective catalyst based on a chiral terpyridine:: synthesis of new C2-symmetric 2,2′:6′,2-terpyridine ligands and copper-catalyzed enantioselective cyclopropanation of alkenes

New C-2-symmetric chiral 2,2':6',2 -terpyridines were prepared from readily available homochiral materials. Copper complexes of these ligands were prepared in situ and their catalytic activities in cyclopropanations of alkenes with alkyl diazoacetate to give cyclopropyl esters were studied. In all cases, the cyclopropyl ester yields were excellent and enantioselectivities up to 94% ee were observed. Competition experiments revealed that electron-donating substituents on styrene accelerate the reaction. A Hammett plot exhibited a good linearity with a negative rho(+) value (-0.79). (C) 2000 Elsevier Science Ltd. All rights reserved.