Nucleophilic ability of 5-aminopyrazoles in the multicomponent synthesis of pyrazolodihydropyridines and pyrazolodihydropyrimidines

Abstract

The nucleophilic ability of substituted 5-aminopyrazoles and the type of dicarbonyl component were investigated to synthesise various pyrazolodihydropyridines and pyrazolodihydropyrimidines. In this multicomponent reaction, two possible reaction mechanisms are proposed to elucidate the importance of the nucleophilic positions in the 5-aminopyrazole molecule leading to the different cyclocondensation products. The extent of the nucleophilicity of the C4-position (β-position of the enamine moiety), the lone pairs of the N1-atom and the NH2 group in the pyrazole molecule affect the reaction time and type of product formed. The acidity of the CH2 moiety of the β-dicarbonyl compound may affect the type of product formed. 1H and 13C NMR data and the X-ray crystal structure analysis support the experimental work and the formed product type.

Keywords: 5-Aminopyrazoles, cyclocondensation, Knoevenagel condensation, multicomponent reactions, Nucleophilic ability, pyrazolodihydropyridines, pyrazolodihydropyrimidines.