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Electrochemical reduction (ECR) and oxidation (ECO) of 5,6,7,8‐tetrafluoroquinoxaline (1) and its derivatives bearing various substituents R (7‐H (2), 7,8‐H2 (3), 6‐CF3 (4), 6‐Cl (5), 5,7‐Cl2 (6), 5‐NH2 (7), 6‐OCH3 (8), 6,7‐(OCH3)2 (9), 6,7,8‐(OCH3)3 (10), 5,6,7,8‐(OCH3)4 (11), 6‐OCH3,7‐N(CH3)2 (12), 6‐N(CH3)2 (13), 6,7‐(N(CH3)2)2 (14), 5,6,7‐(N(CH3)2)3 (15), and 7,8‐cyclo‐(=CF‐CF = CF‐CF=) (16)) in the carbocycle have been studied by cyclic voltammetry in MeCN. For 1–4 and 7–15, the first reduction peaks have been found to be 1‐electron and reversible, thus corresponding to the formation of their radical anions (RAs), which are long lived at 295 K except those of 4–6 and 15, 16. Irreversible hydrodechlorination has been observed for 5 and 6 at the first step of their ECR confirmed by EPR detection of corresponding RAs of 2 and 5,7‐H2 derivative of 1 (17) at the next steps. Electrochemically generated RAs of 1–3, 7–14, and 17 have been characterized in MeCN by EPR spectroscopy together with DFT calculations at the (U)B3LYP/6‐31 + G(d) level of theory using PCM to describe the solvent. A noticeable alternation of spin density on the –NCCN– moiety of quinoxaline has been observed for all RAs possessing R‐substitution asymmetry. The comparative electron‐accepting ability of 1–15 has been analyzed in terms of their experimental reduction peak potentials and the (U)B3LYP/6‐31 + G(d)‐calculated gas‐phase first adiabatic electron affinities (EAs). The differences in electron transfer solvation energies for 1–15 have been evaluated on the basis of ECR peaks' potentials and calculated gas‐phase EAs. The ECO of 1–5 and 7–14 has been found to be irreversible.

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In this paper, we considered the opportunity to use microwave irradiation as an alternative to the convection heating method during the guaiacol condensation reaction with glyoxalic acid in an aqueous solution in the presence of sodium hydroxide in order to preparatively obtain the 4-hydroxy-3-methoxymindic acid, an intermediate of the vanillin synthesis. The experiments under the influence of the microwave irradiation were carried out using the «Speedwave four» microwave system that allowed varying the irradiation power in the range from 0 to 1450 W. The condensation reaction was carried out at the irradiation power of 290, 580, 870, and 1160 W. The effects of time, temperature and microwave radiation power on the desired product yield of the condensation reaction was established by varying the reaction conditions during the experiments. Using this method, the experimental conditions of highest product yield were determined when temperature of the reaction mixture, the irradiation power and synthesis time were 70 ºC, 870 W, and 30 minutes respectively. A comparison of the results of the synthesis of 4-hydroxy-3-methoxymindic acid under the microwave activation and for the conventional procedure was performed. The use of the microwave irradiation was found to significantly reduce (up to 20 times) the synthesis time, however, the maximum product yield achieved by this method turned out to be lower compared to the one obtained by conventional procedure. The 4-hydroxy-3-methoxymindic acid synthesized samples structure was confirmed using IR, 1H and 13C NMR spectroscopy.