Studies on the Regio- and Stereoselectivity of Halohydroxylation of 1,2-Allenyl Sulfides or Selenides

It was observed that the halohydroxylation of 1,2-allenyl sulfides or selenides with Br2 (CuBr2 or
NBS) or I2 and water demonstrated a fairly good regioselectivity (i.e., the CC bond that is remote
from the S or Se atom was halohydroxylated with the halogen atom connecting to the middle carbon
atom and the hydroxyl group connecting to the non-S terminal carbon or Se-substituted terminal
carbon atom of the allene moiety), leading to the synthesis of synthetically important 3-organosulfur
or seleno-2-haloallylic alcohols. The stereoselectivity depends on the nature of X+ and S or Se,
showing a Z-selectivity with the matched Lewis acid−base pair.