Oxidation with DMSO
Oxidation of Alcohols by Activated Dimethyl Sulfoxide and Related Reactions, an Update,
Tidwell, T. T. Synthesis 1990, 10, 857.
Oxidation of Alcohols to Carbonyl Compounds via Alkoxysulfonium Ylides: The Moffatt, Swern and Related Reactions,
Tidwell, T. T. Org. Reactions, 1990, 39, 297.
DMSO in combination with an activating agent (usually an acylating agent or an acid) and an amine base is a very mild and selective reagent for oxidation of alcohols to aldehydes and ketones. Over-oxidation of aldehydes is not a problem. The reagent does not cleave glycols and α-hydroxy carbonyl compounds like the transition metal oxidants (Cr, Ru, Os, Mn) and even the otherwise very selective Dess-Martin periodinane will sometimes do.
Oxidation of Sensitive Substrates with DMSO-Lewis Acid (Moffat, Swern)
The oxidation was discovered by Moffat, who used acetic anhydride to activate the DMSO. However, a number of subsequent modifications which improved the procedure have become named reactions also. These differ in how the active intermediate Me2S-X A is generated. They include the Parikh-Doering (Py·SO3 + DMSO), Pfitzner-Moffat (carbodimides + DMSO), Corey-Kim (dimethyl sulfide and chlorine) and Swern (DMSO + oxalyl chloride or DMSO + trifluoroacetic anhydride) oxidations. Of these the procedure introduced by Swern using oxalyl chloride and triethylamine to activate the DMSO is by far the most popular one, so the reaction is often referred to as a Swern oxidation. Less commonly used is the Kornblum oxidation, in which the intermediate alkoxy sulfonium salt B is prepared by O-alkylation of DMSO by an allyl or benzyl halide.
Even aldehydes too unstable to be isolated can be prepared, since the reaction mixtures can be directly used for subsequent transformations, as in the two examples below. α-Keto Aldehydes: Ireland J. Org. Chem. 1985, 50, 2198.
Formyl silanes are very unstable and can typically not be isolated. Here an in situ-formed aldehyde is trapped with a lithium reagent. Ireland J. Org. Chem. 1985, 50, 2198; Linderman J. Org. Chem. 1988, 53, 1569
DMSO oxidants do not oxidize sulfides to sulfoxides, or amines to amine oxides, which can be a problem for oxidation of sulfide-containing alcohols with many other oxidants. Breynolide: Smith, A. B. III et al. J. Am. Chem. Soc., 1991, 113, 4037. DOI J. Am. Chem. Soc., 1992, 114, 9419-9434.
