Cyclization of Isothiosemicarbazones. IV. Synthesis of the [1,2,4]Triazolo[1,5-c]pyrimidine Ring System

Condensation of isothiosemicarbazones with ethoxymethylenemalononitrile gave 2,3-dihydro[1,2,4] triazolo[1,5-c]pyrimidines in moderate to high yields. The 2,3-dihydro compounds were readily oxidized in dimethyl sulfoxide to give the corresponding [1,2,4]triazolo[1,5-c]pyrimidines.