Parikh–Doering oxidation

[1] The procedure uses dimethyl sulfoxide (DMSO) as the oxidant and the solvent, activated by the sulfur trioxide pyridine complex (SO3•C5H5N) in the presence of triethylamine or diisopropylethylamine as base.

[2] However, the Parikh–Doering oxidation sometimes requires a large excess of DMSO, SO3•C5H5N and/or base as well as prolonged reaction times for high conversions and yields to be obtained.

Nucleophilic attack by alcohol 4 and deprotonation by pyridine (5) gives intermediate 6, an alkoxysulfonium ion associated with the anionic pyridinium sulfate complex.

The addition of at least two equivalents of base deprotonates the alkoxysulfonium ion to give sulfur ylide 7 and removes the pyridinium sulfate counterion.

In the last step, the ylide goes through a five-membered ring transition state to give the desired ketone or aldehyde 8, as well as an equivalent of dimethyl sulfide.