Deprotonation of 2 with TlOEt and subsequent S-alkylation of the thallium(I) salt with methyl iodide gave (phenylsulfonyl)ketene dimethyl dithioacetal moxonide (5). When other bases were used in the deprotonation step deoxygenated products, viz. C 6 H 5 SO 2 CH C(SCH 3 ) 2 were obtained. Evidence is presented that oxygen is lost by an intramolecular redox reaction of an initially formed vinylsulfenic ester. ... The new ketene dithioacetal monoxide 5 reacts with ...