Optically Active Seleninate Esters: Isolation, Absolute Configuration, Racemization Mechanism, and Transformation into Chiral Selenoxide

Optically active seleninate esters were obtained for the first time by chromatographic resolution
on an optically active column. The absolute configurations of the optically active seleninate esters
were determined by comparing their chiroptical properties with those of two analogous sulfinate
esters, the absolute configuration of one of which is known and that of the other was determined
by X-ray crystallographic analysis. The optically active seleninate esters were found to racemize
in solution. Kinetic studies of the racemization, the oxygen exchange reaction with H218O, and
theoretical studies clarified that the racemization of the optically active seleninate esters in solution
proceeded via an achiral hypervalent selenurane intermediate that was formed by the reaction
with water. The reaction of the optically active seleninate ester and the sulfinate ester having
bulky substituents with Grignard reagents was found to proceed with the retention of stereochemistry to give an optically active selenoxide and sulfoxides, respectively.