Oxidation of Alcohols to Carbonyl Compounds with Activated Dimethyl Sulfoxide via Alkoxysulfonium Ylides. The Swern, Moffatt, and Related Oxidations

Oxidation of Alcohols to Carbonyl Compounds with Activated Dimethyl Sulfoxide via Alkoxysulfonium Ylides. The Swern, Moffatt, and Related Oxidations 

Mild oxidation of alcohols to carbonyl compounds via alkoxysulfonium ylides is a very important transformation in organic synthesis and several reviews cover many of the practical and mechanistic aspects of the Moffatt, Swern, and related oxidations [1316-1320]. 

Swern oxidation has been the procedure of choice in several multistep syntheses of key intermediates en route to natural products [1321, 1322] or therapeutic agents [1323-1329], 

Dimethyl sulfoxide 1787 undergoes reactions in which nucleophilic attack occurs on the sulfur atom. The lone pair of electrons on sulfur, however, cannot be expected to favor the approach of a nucleophile, in spite of the presence of a partial positive charge and vacant d orbitals on the sulfur. Therefore, it is not surprising that most reactions in which nucleophilic attack takes place readily on sulfur are aided by prior electrophilic attack on the oxygen atom to give dimethylsulfonium species 1788. A nucleophile can now perform a facile displacement on sulfur with departure of a leaving group. The formation of the sulfonium species 1789 is usually followed by further reactions. 

Activation of dimethyl sulfoxide by oxalyl chloride, as developed by Swern and co-workers [1317-1319,1335,1371-1373], has become the most used of these oxidation procedures, but several of the other methods are also convenient and effi-dent. The usual nudeophiles have been alcohols, phenols, enols, amines, and oximes. 

---