Reactions

First, the oxygen atom of DMSO attacks one carbonyl carbon of oxalyl chloride, displacing a chloride ion and forming a chlorosulfonium intermediate. This intermediate loses CO₂ and CO, generating a chlorodimethylsulfonium ion (Me₂S⁺-Cl^-), which is the active oxidizing species. The alcohol attacks the electrophilic sulfur of the chlorodimethylsulfonium ion, displacing chloride and forming an alkoxysulfonium intermediate.The base (Et₃N) deprotonates one of the methyl groups of the sulfonium ion, triggering a [1,2]-elimination. The electrons from the C–H bond of the methyl group flow toward the sulfur, simultaneously breaking the O–C bond of the substrate.The elimination yields the carbonyl compound (aldehyde or ketone), dimethylsulfide (Me₂S), and triethylammonium salt.