Novel aspects in the reaction of 2-diazo-2′-(phenylthio)acetophenone with arenesulphenyl chlorides: formation of α-ketoaldehyde thioacetal chlorides via cyclic sulphonium α-(arylthio)phenacylides

Abstract

Under conditions where 2-diazoacetophenone and benzenesulphenyl chloride provide 2-chloro-2-(phenylthio)-acetophenone, 2-diazo-2′-(phenylthio)acetophenone (1a) with 2-nitro- and 2,4-dinitro-benzenesulphenyl chlorides gives, after treatment with water, 2-(2-nitrophenylthio)- and 2-(2,4-dinitrophenylthio)-3-oxo-1-phenylbenzo[b]thiophenium-2-ides (4b and c) respectively. The structure of these ylides was established by independent syntheses from 3-oxo-1-phenylbenzo[b]thiophenium-2-ide (4a) and the appropriate arenesulphenyl chloride in the presence of triethylamine. In contrast, two molecular proportions of benzenesulphenyl chloride were required to liberate the diazo nitrogen from the phenylthio-diazoketone (1a) when there resulted hydrogen chloride and 2-chloro-2,2,2′-tris(phenylthio)acetophenone (5a). The latter was also prepared from benzenesulphenyl chloride and 3-oxo-1-phenyl-2-(phenylthio)benzo[b]thiophenium-2-ide (4d), which was readily synthesised by condensation of the unsubstituted ylide (4a) with N-(phenylthio)phthalimide in the presence of triethylamine. 2-Chloro-2,2-bis(phenylthio)acetophenones have apparently not been reported previously; evidence in support of such a structure was obtained by hydrolysis, with boiling water, of 2-chloro-2,2,2′-tris(phenylthio)acetophenone (5a) to hydrogen chloride, benzenethiol and S-phenyl [2-(phenylthio)phenyl]thioglyoxylate (8a).