Synthesis of masked 2-amino-6-methyl-4-oxo-4H-pyran-3-carbaldehydes

Acetoacetylation of (1,3-dimethylbenzimidazol-2-ylidene)-, (3-methylbenzothiazol-2-ylidene)-, and (3,4-dimethylthiazol-2-ylidene) acetonitriles with 2,2,6-trimethyl-4H-1,3-dioxin-4-one was found to yield appropriate C-acylation products. Treatment of the obtained products with perchloric acid afforded 2-(2-amino-6-methyl-4H-pyran-4-one-3-yl) substituted quaternary azolium salts. Their reduction with 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 aldehyde.