Stereochemistry of dithiirane 1-xxides: Optical resolution, absolute configuration, and racemization and isomerization of dithiirane 1-oxides

Article abstract of DOI:10.1016/S0040-4020(97)00553-X

Optical resolution of (1RS, 3SR)-(1) and (1RS, 3RS)-(2) dithiirane 1-oxides was achieved by HPLC equipped with a chiral column to give 1a and 1b and 2a and 2b, respectively. X-ray analyses proved absolute configurations of in and 1b to be (1R, 3S) and (1S, 3R), while those of 2a and 2b were determined to be (1R, 3R) and(1S, 3S), respectively, since 2a and 2b isomerized stereospecifically to 1b and 1a, respectively. Enantiomeric dithiirane 1-oxides la and 1b racemized to each other whereas 2a and 2b did not. To the racemization (oxygen migration) is proposed a mechanism involving homolysis of the S(O)-S bond at the initial step followed by a ring closure giving a 1,2,4-oxathietane intermediate. Isomerization between 1 and 2 was inhibited by a radical scavenger, DPPH.