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

2003-03-26T00:00:00Z (GMT) by Shengming Ma Hongjun Ren Qi Wei
A highly regio- and stereoselective halohydroxylation of 1,2-allenyl sulfoxides with X<sup>+</sup> and water was developed. The reaction shows <i>E</i>-stereoselectivity. In the iodohydroxylation reaction, I<sub>2</sub> was used to introduce the iodine atom. For bromohalohydroxylation, CuBr<sub>2</sub>, NBS, or Br<sub>2</sub> can be used. When using I<sub>2</sub>, NBS, or Br<sub>2</sub>, the addition of LiOAc·2H<sub>2</sub>O is necessary for high yields of the halohydroxylation products. The chlorohydroxylation reaction was preformed by milling 1,2-allenyl sulfoxides and CuCl<sub>2</sub>·2H<sub>2</sub>O with silica gel. Under the catalysis of a Pd(0) complex, the halohydroxylation products, that is, <i>E</i>-2-halo-1-phenylsulfinyl-1-alken-3-ols, can undergo Sonogashira, Suzuki, and Negishi cross-coupling reactions leading to <i>Z</i>-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 <i>E</i>-halohydroxylation and a selective Pd- or Ni-coupling reaction.