Synthesis of Dialkyl 2-(2-Hydroxyphenyl)-4,6-dimethyl-1,2-dihydropyridine-3,5-dicarboxylates and Alkyl 2,4-Dimethyl-5-oxo-5H-benzopyrano-pyridine-3-carboxylates

Article abstract of DOI:10.1055/s-1987-27984

The reaction of 2-hydroxybenzaldehydes with 3-oxobutanoic esters and excess ammonia in acetic acid at room temperature yields dialkyl 2-(2-hydroxyphenyl)-4,6-dimethyl-1,2-dihydropyridine-3,5-dicarboxylates and their 2-(3,5-dialkoxycarbonyl-4,6-dimethyl-1,2,3-trihydropyridinium-2-yl)-phenoxide zwitterions.Mild oxidation of these compounds is accompanied by lactonisation, with formation of alkyl 2,4-dimethyl-5-oxo-5H-<1>benzopyrano<4,3-b>pyridine-3-carboxylates, which had previously been incorrectly formulated.Reaction of other o-substituted benzaldehydes with alkyl 3-aminocrotonates in acetic acid at room temperature also yields dialkyl 2-aryl-4,6-dimethyl-1,2-dihydropyridine-3,5-dicarboxylates, as well as the normal 1,4-dihydropyridine Hantzsch esters.