We describe the synthetically useful enantioselective addition of Br-CX3 (X=Cl or Br) to terminal olefins to introduce a trihalomethyl group and generate 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)RhII BrCl] complex by a benzylic radical intermediate. This mechanism appears unprecedented in asymmetric catalysis.
Keywords: alkenes; asymmetric catalysis; enantioselectivity; radical reactions; rhodium.
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