Brand new quantitative solid-state synthesis of N-pyrazolyl azomethines

Abstract

Fifteen preparatively useful azomethines 3 and 5 have been quantitatively (100% yield at 100% conversion) obtained as hydrates by ball-milling together 4-aminoantipyrine 1 and 3-amino-4,6-dimethylpyrazolopyridine 4 with solid benzaldehydes 2 without passing through liquid phases. Unlike (acid catalysed) azomethine syntheses in solution, the solid-solid condensations proceed "waste free" in the absence of any auxiliaries or microwave irradiation. The product yields are quantitative in all cases and the products do not require purifying workup.