Sulfonium-based oxidation of alcohols to aldehydes

However, the reactions are not too popular with many undergraduate chemistry students in the laboratory since the common byproduct dimethylsulfide is a strong odorant, reminiscent of fouling eggs, that requires a well-ventilated fume hood.

Other drawbacks might include excess of base, handling of the dehydrating agent, limited choice of solvent or side reactions at elevated temperature, e.g. Pummerer rearrangement or elimination of the sulfonium intermediate to the reactive H2C=(S+)-CH3-species that form methylthiomethyl ethers with alcohols.

The sulfonium oxidations can be categorized into two groups: The methods discovered earliest rely on activated alcohols like alkyl tosylates (Kornblum oxidation)[2] or alkyl chloroformates (from reaction of alcohols with phosgene: Barton-Kornblum)[3] that react as electrophiles when treated with DMSO, liberating an oxygenated leaving group (e.g. OTs−).

Depicted below is the activated sulfoxide generated during Swern oxidation 4 reacting with a secondary alcohol 5 to form alkoxysulfonium species 6.

These activated sulfoxides react as electrophiles when treated with an alcohol, expelling a leaving group that might simultaneously function as counter-ion to the alkoxysulfonium species (RO−SMe+2) generated.