Studies on electrophilic reaction of Br2 with 1,2-allenylic sulfones. A highly regio- and stereoselective synthesis of 1-phenylsulfonyl-2-bromo-1(E)-alken-3-ols and 1-phenylsulfonyl-2-bromo-1(E),3(E)-butadienes

The reaction of 1,2-allenyl sulfones with Br2 afforded E-bromohydroxylation- or E-bromination–elimination products highly regio- and stereoselectively depending on the substitution pattern of the allene functionality. The five-membered intermediate cis-3h was isolated and characterized by X-ray diffraction study. The study on its reactivity of this intermediate revealed the origin of the regio- and stereoselectivity of this reaction.