Reactions of 2-Aminoimidazo-1,3,4-thiadiazoles with Ethyl Dicarboxylates in Polyphosphoric Acid (PPA)

Article abstract of DOI:10.1002/ardp.19823150105

The 2-amino-6-arylimidazo<2,1-b>-1,3,4-thiadiazoles 1d,e cyclise on heating in polyphosphoric acid (PPA) with ethyl malonate or ethyl diethylmalonate to yield the 2-aryl-6,8-dioxodihydro-6H-imidazo<2,1-b>-1,3,4-thiazolo<3,2-a> pyrimidines 3d,e or the 7,7-diethyl compounds 4d,e.Compounds 1a-f cyclise in PPA with ethyl succinate or ethyl phthalate to yield the 6-aryl-2-succinimido- or 6-aryl-2-phthalimido-imidazo<2,1-b>-1,3,4-thiadiazoles 5a, b, d-f and 6a-f.Compounds 1d,e were condensed with ethyl oxalate to yield the 2-(ethoxycarbonyl-formylamino)-6-arylimidazo<2,1-b>-1,3,4-thiadiazoles 7d,e.Ethyl levulinate with 1d,e in PPA probably forms 6-aryl-2-(2-methyl-5-oxo-Δ³-pyrrolino)imidazo<2,1-b>-1,3,4-thiadiazoles.