Asymmetric Radical Reaction in the Coordination Sphere. III. Asymmetric Addition of Trichloromethanesulfonyl Chloride and Carbon Tetrachloride to Olefins Catalyzed by a Ruthenium(II) Complex with Chiral Ligand

The asymmetric addition of trichloromethanesulfonyl chloride to styrene in the presence of a catalytic amount of a ruthenium(II) complex with chiral ligands, Ru2Cl4[(−)-diop]3 or Ru2Cl4[(+)-diop]3, proceeds under mild conditions to give optically active 1:1 adducts, 1,1,1,3-tetrachloro-3-phenylpropane (2), with the extrusion of sulfur dioxide. When (−)-DIOP or (+)-DIOP was used as a chiral ligand of the ruthenium(II) complex, (R)-(+)-(2) or (S)-(−)-(2), was obtained with about 10% enantiomeric excess, respectively. A reaction mechanism involving a radical redox transfer mechanism was proposed; the asymmetric induction was attributed to the restricted configuration of the radical intermediates confined in the coordination sphere of the ruthenium complex with chiral ligands.