Screening of N,N-bidentate and N,N,Ntridentate pyridine-based ligands in the catalytic allylic oxidation of cyclic olefins

A variety of chiral N,N-bidentate and N,N,N-tridentate ligands based on the pyridine framework, namely C2-symmetric dipyridylmethane and terpyridine, N-(p-toluensulfinyl)iminopyridines and two kinds of iminopyridines, has been assessed in the asymmetric copper(I)-catalysed allylic oxidation of cyclic olefins. Catalytic activity and enantioselectivity were found to be highly dependent upon the framework of the ligands, which afforded cycloalkenyl benzoates in low to moderate yields and enantioselectivities. The best yields (up to 70%) and enantioselectivities (up to 53% enantiomeric excess) were obtained with an iminopyridine based on camphane and quinoline skeletons.