Remote steric effects of C 2 -symmetric planar-chiral terpyridine ligands on copper-catalyzed asymmetric cyclopropanation reactions

A series of enantioselective cyclopropanation reactions of substituted alkenes with diazoacetates was investigated in the presence of Cu(OTf)2 with C2-symmetric planar-chiral bridged 2,2′:6′,2″-terpyridines. Planar-chiral terpyridine–copper complexes exhibited moderate diastereomeric excesses with good enantioselectivities of cis-cyclopropane products in catalytic asymmetric cyclopropanation reactions of various styrene derivatives with ethyl diazoacetate. A remote steric effect was found to enhance enantioselectivity for the cyclopropanation induced by a sterically demanding substituent beyond the ansa-bridge of pyridinophane ligands on the other side of the reaction site as a relay of steric influences through flexible cyclophane bridges.