Thiophenium 5-ylids

Thiophenium salts and thiophenium ylids, chemistry of, 45, 151 Thiopyrans, 34, 145 59, 179 Thiopyrones (monocyclic sulfur-containing pyrones), 8, 219... 

The first reference to the formation of thiophenium ylids by carbene addition to thiophene appeared in 1972, when Durr and co-workers noted that pyrolysis of diazotetraphenylcyclopentadiene in thiophene resulted in a low yield of the ylid 14, although no information on the yield of the reaction or the physical or spectroscopic properties of 14 were given (72TL1257). 

These two reports clearly demonstrate that thiophene can form ylids, despite the considerably reduced nucleophilicity of the sulfur atom and that stable thiophenium ylids might be found. This was subsequently confirmed with the observation that the photolysis of dimethyl diazomalonate in thiophene result in the formation of 15, which was isolated in low yield as a stable crystalline solid (77JOC3365). It was subsequently demonstrated by my own group that thiophenium bis(alkoxycarbonyl)methylides could be formed in high yield using rhodium(II) acetate-catalyzed addition of diazomalonate... 

Porter, A. E. A., The Chemistry ofThio-phenium Salts and Thiophenium Ylids, 45, 151. 

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