Synthesis of 6-Amino-2-bromo-4-hydroxynicotinaldehyde Derivatives

摘要

Acylation of (1,3-dimethylbenzimidazol-2-ylidene)-, (3-methylbenzothiazol-2-ylidene)-, and (3,4-dimethylthiazol-2-ylidene)-acetonitriles with l-(cyanoacetyl)-3,5-dimethylpyrazole was found to proceed at the exocyclic carbon atom, yielding the appropriate 2-heterylidene-3-oxopentanedinitriles. Treatment of the prepared dinitriles with hydrobromic acid in refiuxing acetic acid afforded 2-(6-amino-2-bromo-4-hydroxypyridin-3-yl)-substituted quaternary salts of benzimidazolium, benzothiazolium, and thiazo-lium. Their structures were confirmed unambiguously by X-ray crystallographic studies. Reduction of these quaternary salts with excess sodium borohydride yielded the corresponding dihydro (in the case of benzoazoles) or tetrahydro (in the case of thiazole) derivatives, which were shown to be synthetic equivalents of the title nicotinaldehyde.