Oxidation of alcohols by “activated” dimethyl sulfoxide. a preparative, steric and mechanistic study

The oxidation of primary, secondary, allylic, benzylic, hindered and bicyclic alcohols with dimethyl sulfoxide (DMSO) “activated” by numerous electrophiles was studied: yields of carbonyls, by-products and recovered alcohols were quantitatively determined. Pathways for carbonyl and by-product formation are presented. Generally, yields of carbonyls increase with increased steric hindrance in the alcohols. Steric effects of tertiary amines, used for basification, were also investigated, and the results are consistent with the suggested reaction pathways. Among previously unreported “activators,” oxalyl chloride is the most generally effective; yields of carbonyls are typically over 95%. Thionyl chloride is also a satisfactory “activator” although yields of carbonyls are not quite as high. An improved method of preparation of alkyl methylthiomethyl ethers, by-products of the oxidation process, is reported.