Formation of 5-alkylidenepyrazol-4(1H)-ones and 3-amino-6-aryl-5-cyano-pyridazine-4-carboxylates from arenealdehyde thiosemicarbazones and unsaturated 1,2-diesters

Abstract

The reaction of arenealdehyde 4-phenylthiosemicarbazones 1a–f with dimethyl ethynedicarboxylate (6) gave methyl [3-aryl-4-oxo-1-(phenylthiocarbamoyl)-4,5-dihydro-1H-pyrazol-5-ylidene]ethanoates 10a–f in 73-79% yield, while, by reaction with diethyl (E)-2,3-dicyanobutenedioate (7), compounds 1a–f are transformed into ethyl [3-aryl-4-oxo-1-(phenylthiocarbamoyl)-4,5-dihydro-1H-pyrazol-5-ylidene]cyanoacetates 15a–f (54-61%) and ethyl 3-amino-6-aryl-5-cyanopyridazine-4-carboxylates 24a–f (22-26%). Rationales for these transformations are presented.