Carbenoid insertions into benzylic C–H bonds with heterogeneous copper catalysts

The copper complexes with bis(oxazoline) or azabis(oxazoline) ligands, once supported on laponite clay by electrostatic interactions, are able to catalyze the insertion of carbenoids in benzylic C–H bonds. In contrast with rhodium catalysts, they are more active with tertiary than with secondary bonds, through a similar mechanism as shown by Hammet correlation. Enantioselectivities are only moderate, with values up to 50% ee. The immobilized catalysts are partially recoverable and the best results are obtained in the case of reactions with high chemoselectivity.