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

A new chiral dirhodium tetracarboxylate catalyst, Rh2( 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 C4 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.