Reaction of quinaldine with 4,6-di(tert-butyl)-3-nitro-1,2-benzoquinone. Dependence of the outcome on the reaction conditions and a deeper insight into the mechanism

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Condensation of quinaldine with 4,6-di ( tert -butyl)-3-nitro-1,2-benzoquinone results in the formation of 5,7-di ( tert -butyl)-2-(quinoline-2-yl)-1,3-tropolone, 5,7-di ( tert -butyl)-4-nitro-2-(quinoline-2-yl)-1,3-tropolone, 3,3-dimethyl-2-(5-hydroxy-4-nitro-3- tert -butyl-6-quinoline-2-yl-pyridine-2-yl)butanoic acid, 6-(2,2-dimethylprop-3-yl)-5- tert -butyl-4-nitro-2-(quinoline-2-yl)-pyridine-3-ol, 1,7-di ( tert -butyl)-3-(quinoline-2-yl)-2-azabicyclo-[3.3.0]octa-2,7-diene-4,6-dione- N -oxide. The formation of 1,3-tropolone and pyridine-2-yl butanoic acid derivatives proceeds through a ring expansion and 2-azabicyclo [3.3.0]octa-2,7-diene-4,6-dione- N -oxide via the contraction of the o-quinone ring. The structure of the heterocyclic compounds obtained was justified by X-ray diffraction analysis, NMR spectroscopy, IR- and HRMS-spectrometry, and the proposed mechanisms of their formation include the participation of an intermediate product of the expansion reaction of the o -quinone cycle - 5,7-di ( tert -butyl)-4-nitro-2-(quinoline-2-yl)-cyclohepta-1,3,5-triene-1,3-diol, which was first isolated preparatively. The DFT/B3LYP/6–311++G** methods were used to determine the thermodynamic stability of tautomeric forms of intermediate products, as well as the relative stability of NH and OH tautomers of 5,7-di ( tert -butyl)-2-(quinolin-2-yl)-1,3-tropolone and 5,7-di ( tert -butyl)-4-nitro-2-(quinolin-2-yl)-1,3-tropolone.