Rearrangement mechanisms of 1,3-dithiolane sulfoxides

Oxidation of sulfide 4 gave a mixture of cis and trans monosulfoxides 5 and 6 as major and minor products, respectively, plus a small amount of disulfoxides 7. The structural assignments of cis and trans sulfoxides 5 and 6 were based on 1H NMR spectroscopy and the regiospecific deuterations of the two isomers . Under neutral conditions cis sulfoxides 5 underwent a sigmatropic rearrangement with 2-methylene hydrogens to give sulfenic acids 18, followed by cyclization to dihydro-1,4-dithiins 2. The trans sulfoxides 6 rearranged involving 2-methyl hydrogens to form isomeric dihydrodithiins 3 via sulfenic acids 19. In the reactions of both the sulfoxides, sulfoxides 4 and disulfides 11 were also formed as minor side products. In the presence of acid catalyst cis sulfoxides 5 produced 2 in quantitative yields plus a small amount of 3 , while the trans sulfoxides 6 gave 2 as major product and 3 as minor. The mechanisms of formation of 2, 3, 4 and 11 are discussed.