Swern Oxidation

In 1976, when treating dimethyl sulfoxide (DMSO) with trifluoroacetic anhydride (TFAA) below -50°C in dichloromethane, D.Swern and co-workers discovered that trifluoroacetoxydimethylsulfonium trifluoroacetate was formed, which reacted rapidly with primary and secondary amines. The resulting alkoxydimethylsulfonium trifluoroacetates, when treated with trimethylamine, formed the corresponding aldehydes and ketones in high yields.

In 1978, oxalyl chloride was found to be more efficient than TFAA as an activating agent for DMSO in the oxidation of alcohols. Since then, the oxidation of primary or secondary alcohols using either DMSO and TFAA or oxalyl chloride has become known as the Swern Oxidation.

The total synthesis of the mytotoxic (+)-aseltoxin utilized the Swern oxidation, as did that of the marine dolabellane diterpene, (+)-deoxyneodolabelline. In the latter case, both Dess-Martin and Ley oxidations were tried, but the substrate suffered carbon-carbon bond cleavage.