Inversion barriers in sulfoxide functions studied by enantioselective liquid chromatography and chiroptical methods

A series of 2-substituted 1,3,2-benzodithiazole 1-oxides has been synthesized and the compounds resolved into enantiomers by semipreparative enantioselective liquid chromatography. The low enantiomerization barriers have been determined by chiroptical techniques and were found to be relatively independent of the 2-substituent used. The kinetic results are consistent with a pyramidal inversion mechanism and a reduced barrier due to electronic effects, favouring the transition state over the pyramidal ground state. This mechanistic rationale was further supported by data obtained from molecular modelling using AM1 geometry optimization. The absolute configurations have been determined via a comparison of their CD-spectra with those of analogs with previously determined configuration. Chirality 9:638–642, 1997.