Condensation of 4-substituted-but-3-en-2-ones (1) with ethyl oxalate gave ethyl 6-aryl-2,4-dioxo-62-hexenoates (2) and were interconverted to the methyl esters by alcoholysis. Compounds (2) were converted by hydrazine or arylhydrazine into the corresponding ethyl 1-H/aryl-5-substituted-pyrazole­3-carboxylates (3), which were hydrolysed to the acids (4). With hydroxyl­ami ne, the ethyl hexenoates (2) afforded 3 ,5-di subs tituted-i soxazo 1 es (5), whereas, with o-phenylenediamine they gave oxyquinoxaline derivatives (6).The 1,3-di keto-es ters (2) on reacti on with acyl hydrazi nes gave the acylhydrazones (7) which were cyclized to the corresponding N-acylpyrazoles (8). Reaction of (1) with arylhydrazines afforded the corresponding hydra­zones (9) which on boiling with ethanol containing two drops of HCl underwent cycl ization to the pyrazol ines (10). Oxidation of (10) with an excess of bromine-water produced the brominated pyrazole derivatives (11). Furthermore, the condensa t i on of the ex,8 -unsa tura ted ketones (1) with acyl hydrazi nes furnished the corresponding hydrazones (12).