Domino-reactions of 3-methyl-5-aminopyrazole with 1-phenyl-3-(4-alkoxyphenyl)pyrazole-4-carbaldehydes and 2,2-dimethyl-1,3-dioxane-4,6-dione

Abstract

Aim. To synthesize 1-phenyl-3-(4-alkoxyphenyl)pyrazole-4-carbaldehydes and determine the direction of their interaction in the three-component condensation with 3-methyl-5-aminopyrazole and 2,2-dimethyl-1,3-dioxane-4,6-dione. Results and discussion. A series of 1-phenyl-3-(4-alkoxyphenyl)pyrazole-4-carbaldehydes was synthesized from arylhydrazone by the Vilsmeier–Haak reaction. The domino-reactions of these aldehydes with 3-methyl-5-aminopyrazole and 2,2-dimethyl-1,3-dioxane-4,6-dione lead to pyrazolo[3,4-b]pyridone systems. Experimental part. The synthesis of 1-phenyl-3-(4-alkoxyphenyl)pyrazole-4-carbaldehyde was carried out by formylation of arylhydrazones under the conditions of the Vilsmeier–Haack reaction with the yield of 55 – 88 %. Refluxing in 2-propanol equimolar amounts of these aldehydes, 3-methyl-5-aminopyrazole and 2,2-dimethyl-1,3-dioxane-4,6-dione gave 3-methyl-4-(1',3'-diarylpyrazol-4'-yl)tetrahydropyrazolo[3,4-b]pyridin-6-ones with the yield of 48 – 75 %. The structure and composition of all substances synthesized were proven by 1 H NMR, IR-spectra and elemental analysis. Conclusions. It has been found that the reactions of 1,3-diaryl substituted pyrazole-4-carbaldehydes with 3-methyl-5-aminopyrazole and 2,2-dimethyl-1,3-dioxane-4,6-dione are regioselective and lead to the formation of pyrazolo[3,4-b]pyridone systems. This orientation of the process corresponds to the interaction of the β-carbon atom of the probable intermediate, which is formed at the first stage of the reaction from dioxandione and aldehyde, with the carbon nucleophilic center in the aminoazole molecule, and then the exocyclic amino group in the heterylamine attacks the C=O group in the dioxane-4,6-dione fragment.