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.
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