Catalyst-Controlled Selective Functionalization of Unactivated C–H Bonds in the Presence of Electronically Activated C–H Bonds

A new chiral dirhodium tetracarboxylate catalyst, Rh_2(S-2-Cl-5-BrTPCP)_4, has been developed for C–H functionalization reactions by means of donor/acceptor carbene intermediates. The dirhodium catalyst contains four (S)-1-(2-chloro-5-bromophenyl)-2,2-diphenylcyclopropane-1-carboxylate ligands, in which all four 2-chloro-5-bromophenyl groups are on the same face of the catalyst, leading to a structure, which is close to C_4 symmetric. The catalyst induces highly site selective functionalization of remote, unactivated methylene C–H bonds even in the presence of electronically activated benzylic C–H bonds, which are typically favored using earlier established dirhodium catalysts, and the reactions proceed with high levels of diastereo- and enantioselectivity. This C–H functionalization method is applicable to a variety of aryl and heteroaryl derivatives. Furthermore, the potential of this methodology was illustrated by sequential C–H functionalization reactions to access the macrocyclic core of the cylindrocyclophane class of natural products