A study on the reactions of some ketenes with 1-aroyl-1H-pyrazoles

Abstract

1-Aroyl-3,4,5-trimethyl-1H-pyrazoles (1a–c) react with diphenylketene (DPK) to afford the enol esters (2); this was confirmed by X-ray analysis. From the reaction of the pyrazoles (1) with dichloroketene (DCK) the pyrazolylpropanediones (3) are isolated, whereas from the reaction with dimethylketene (DMK) both the enol esters (2) and the pyrazolylpropanediones (3) were obtained. The hydrolysis of the products (3) was also studied. The corresponding pyrazolylpropanediones (10) and the enol esters (11) or their degradation products (12) were isolated from the reactions of the pyrazoles (1a–c) with some mixed anhydrides (9) in the presence of triethylamine. The structure of (10e) has also been confirmed by X-ray crystallography. Plausible schemes accounting for the formation of the products, involving as a common step the quaternization of N-1 are envisaged.