Imidoyl-substituted oxosulphonium ylides: preparation and reaction with nitrile oxides

The N-arylbenzimidoyloxosulphonium ylides (3) have been isolated from the reaction of dimethyloxosulphonium methylide with N-arylbenzimidoyl chlorides. The crystalline oxosulphonium ylides (4) and (5) were similarly prepared from 2-chloropyrimidine and 3-chlorobenzisothiazole 1,1-dioxide, respectively. The ylides (3) reacted with nitrile oxides to give pyrazole 2-oxides (6). Dimethyloxosulphonium 4-nitrobenzylide (2) gave a 2 :1 adduct (7) with benzonitrile oxide, but a 1 :1 adduct (8) with benzonitrile N-phenylimide. The relevance of these observations to the mechanism of the reaction of sulphur ylides with nitrile oxides and nitrile imides is discussed.