Interception of a thiocarbonyl ylide by thiouracil and crystal structure of the 2 : 1 adduct

The reaction of thiocarbonyl ylide 1, generated in situ by thermolysis of t he corresponding 2,5-dihydro-1,3,4-thiadiazole, with a twofold excess of th iouracil ( I) yielded a mixture of the 1:2 adduct 5 and the 1:1 adduct 6 in a ratio of ca. 1:1. These interception products are formed by protonation of 1 and nucleophilic addition via the S- or O-atom. The structure of 5 has been established by X-ray crystallography.