Ethynyl(trimethyl)silane reacted with N,N-dichloroarenesulfonamides to give unstable N-[2,2-di-chloro-2-(trimethylsilyl)ethylidene]arenesulfonamides which underwent desilylation by the action of amines or ethanol with the formation of N-[(dialkylamino)methylidene]arenesulfonamides and N-(2-methoxyvinyl)arene-sulfonamide.