Acid-induced interaction of 2-diazoacetophenones and sulphides with special reference to the cyclization of 2-diazo-2′-(phenylthio)acetophenones and the unusual formation of a diacylolefin in a reaction between a β-carbonylsulphonium ylide and a phenacylsulphonium salt

Abstract

When treated with a molar excess of perchloric acid, 2-diazo-2′-(phenylthio)acetophenone provides 2,3-dihydro-3-oxo-1-phenylbenzo[b]thiophenium perchlorate, which may be deprotonated by triethylamine or, more slowly, by the diazo-ketone. When the latter is used, the first formed β-carbonylsulphonium ylide reacts with unconsumed salt to provide 1,2-bis-[o-(phenylthio)benzoyl]ethylene. Similar results are obtained with 2′-(p-chlorophenylthio)-2-diazoacetophenone. Previously, such reactions between sulphonium salts and ylides have always provided 1,2,3-triacylcyclopropanes. In the presence of perchloric acid, typical 2-diazoacetophenones react with dimethyl sulphide and with methyl phenyl sulphide to provide the corresponding phenacylsulphonium salts in high yield. With diphenyl sulphide the reaction fails, suggesting that the ready cyclization of 2-diazo-2′-(phenylthio)acetophenone is a consequence of the juxtaposition of the diazoacetyl and phenylthio-groups.