STUDIES ON THE OXIDATION OF 1,3-DITHIANE AND 5,5-DISUBSTITUTED ANALOGS INCLUDING X-RAY CRYSTAL-STRUCTURE, EQUILIBRATION STUDIES AND PK(A) MEASUREMENTS ON SELECTED OXIDES

Oxidation of 1,3-dithiane has been carried out using eight different oxidants under several different reaction conditions. The most favourable conditions for obtaining the required trans-1,3-dithiane 1,3-dioxide were to use either MCPBA in Et(2)O or NaIO4 in MeOH-H2O. Other 5,5-disubstituted-1,3-dithianes were also prepared and subjected to similar oxidations. For these compounds the best oxidant for obtaining the trans-dioxides was O-3. A rationalisation for the stereochemical outcome of the oxidations is presented and requires that trans-1,3-dithiane 1,3-dioxide is more stable than cis-1,3-dithiane 1,3-dioxide. This is borne out by equilibration studies of the two diastereoisomeric sulfoxides using N2O4. A rationalisation for the greater stability of the trans compared to the cis isomer is also presented and fits with the pK(a) values and melting points of the two compounds.