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Aromatization of 4,7-Dihydro-6-nitropyrazolo[1,5a]pyrimidines in Near-Electrode Chemical Reactions in DMF Solutions
Lyudmila V Mikhalchenko1, Marina Yu Leonova1, Anastasia A Levina1
1Institute of Organic Chemistry, Russian Academy of Sciences, Leninsky prosp. 47, Moscow 119991, Russia.
Abstract:
The electroreduction (ER) and electrooxidation (EO) of biologically active 6-nitro-4,7-dihydropyrazolo[1,5-a]pyrimidines on a glassy carbon electrode in DMF (N,N-dimethylformamide) solutions containing 0.1 M Bu4NBF4 or Bu4NClO4 supporting electrolytes have been studied by cyclic voltammetry. Protonation of radical anions (RAs) typically occurs via a self-protonation mechanism, wherein the proton donor is the parent molecule that generated the radical anion. The intermediate nitroso-derivative undergoes isomerization and reduction, forming an amine and aromatizing the pyrimidine ring of the compound. Electrochemical oxidation of the compounds proceeds with dehydrogenation and aromatization of the pyrimidine ring, leading to the formation of an aromatic nitro compound. Quantum-chemical calculations have been performed to study the tautomerization reactions of the intermediate compound, the electron density distribution at the Frontier orbitals and their energies, using DFT method. Possible reaction schemes are on both experimental and computational results.
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