The reaction of 6-substituted 4-pyrone-2-carboxylic acids with o-phenylenediamine. Synthesis and structure of 3-(1H-1,5-benzodiazepin-2(3Н)-ylidenemethyl)quinoxalin-2(1H)-ones

 6-Aryl(alkyl)-4-pyrone-2-carboxylic acids upon refluxing in n-BuOH react with two equivalents of о-phenylenediamine, giving 26–85% yields of 3-(1H-1,5-benzodiazepin-2(3H)-ylidenemethyl)quinoxalin-2(1H)-ones, which exist in two tautomeric forms. The direction of the initial nucleophilic attack on the pyrone ring and the tautomeric composition of the obtained products is mainly determined by the substituent at the С-6 atom. Quantum-chemical calculations were used to estimate the stability of tautomers in the gas phase.