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

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.