Highly Regio- and Stereoselective Halohydroxylation Reaction of 1,2-Allenyl Phenyl Sulfoxides. Reaction Scope, Mechanism, and the Corresponding Pd- or Ni-Catalyzed Selective Coupling Reactions

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Abstract
A highly regio- and stereoselective halohydroxylation of 1,2-allenyl sulfoxides with X+ and water was developed. The reaction shows E-stereoselectivity. In the iodohydroxylation reaction, I2 was used to introduce the iodine atom. For bromohalohydroxylation, CuBr2, NBS, or Br2 can be used. When using I2, NBS, or Br2, the addition of LiOAc·2H2O is necessary for high yields of the halohydroxylation products. The chlorohydroxylation reaction was preformed by milling 1,2-allenyl sulfoxides and CuCl2·2H2O with silica gel. Under the catalysis of a Pd(0) complex, the halohydroxylation products, that is, E-2-halo-1-phenylsulfinyl-1-alken-3-ols, can undergo Sonogashira, Suzuki, and Negishi cross-coupling reactions leading to Z-2-substituted-1-phenylsulfonyl-1-alken-3-ols. The C−S bond of the coupling product may undergo a further coupling reaction with organozincs under the catalysis of an Ni catalyst. Here, the presence of a hydroxyl group is important for a smooth coupling involving the C−S bond. Thus, optically active stereodefined multisubstituted allylic alcohols can be prepared by the reaction of the easily available optically active propargylic alcohols with sulfinyl chloride followed by E-halohydroxylation and a selective Pd- or Ni-coupling reaction.

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