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&middot2H2O is necessary for high yields of the halohydroxylation products. The chlorohydroxylation reaction was preformed by milling 1,2-allenyl sulfoxides and CuCl2&middot2H2O 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.