Ring-size effects in the oxidation and reduction of some cyclic sulphoxides

Abstract

The oxidation rates of thietan 1-oxide (1), tetrahydrothiophen 1-oxide (2), and 2H-tetrahydrothiopyran 1-oxide (3) by perbenzoic acid in acidic and alkaline media have been measured in 40 : 60 dioxan-water. The effect of ring size is small, suggesting no major changes in rehybridization at the reaction centre in going from the ground to the transition state. The reduction rates of (1)–(3) and of cis-(4) and trans-4-t-butyl-2H-tetrahydrothiopyran 1-oxide (5) by iodide ion in aqueous perchloric acid solution have also been determined. As the reduction rates show a different dependence on acid concentration for the compounds examined, the interpretation of the ring-size effect is complex. The analysis of reduction rates of compounds (3)–(5) shows that the sulphinyl oxygen atom preferentially occupies the axial position.