Rhodium-Catalyzed Enantioselective Radical Addition of CX4 Reagents to Olefins

摘要

We describe an enantioselective addition of Br-CX3 (X = Cl or Br) to terminal olefins that introduces a trihalomethyl group and generates optically active secondary bromides. Computational and experimental evidence supports an asymmetric atom transfer radical addition (ATRA) mechanism in which the stereodetermining step involves outer-sphere bromine abstraction from a (bisphosphine)Rh(II)BrCl complex by a benzylic radical intermediate. Beyond the synthetic utility, this mechanism appears unprecedented in asymmetric catalysis.