ChemInform Abstract: Study of the Reactivity of α-Acylenaminoketones. Synthesis of Pyrazoles

The reactions of 4-(methylamino)-3-penten-2-one with diazoketones yielded the α-acylenaminoketones 1–3 in good yields. Preparation of the α-acylenaminoketone 4 was carried out by treatment of 4-(t-butyl-amino)-3-penten-2-one with benzoyl chloride being followed by reaction of transamination with methyl-amine. The reactions were carried out in five different solvents and were submitted to gas chromatogra-phy/mass spectrometry analysis, with the goal of obtaining substituted pyrazoles and determining which of the carbonyls would preferentially be attacked by the nucleophile. The reactions of compounds 1–4 with hydrazine reagents led to the formation of the pyrazoles 5–7a-q. Small amounts of 4-methylamino-2-pentenones 10a-q, amides 11a-q and pyrazoles 12a-q were also obtained in these reactions. The unexpected formation of pyrazoles 15d,h,q was detected when methanol and N,N-dimethylformamide were used as solvents in the reactions of α-acylenaminoketone 4 with hydrazine reagents.