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Synthesis 1987; 1987(5): 499-503
DOI: 10.1055/s-1987-27984
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Synthesis of Dialkyl 2-(2-Hydroxyphenyl)-4,6-dimethyl-1,2-dihydropyridine-3,5-dicarboxylates and Alkyl 2,4-Dimethyl-5-oxo-5H-[1]benzopyrano[4,3-b]-pyridine-3-carboxylates

C. N. O'Callaghan*
  • *Medical Research Council of Ireland Laboratories, Chemistry Building, Trinity College, Dublin 2, Ireland
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Publication Date:
18 September 2002 (online)

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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.