Porous carbons-derived from vegetal biomass in the synthesis of quinoxalines. Mechanistic insights.

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Abstract

We report herein for the first-time acid biomass-derived carbons from vegetal biomass, with high developed porosity, prepared through the integrating method comprising pyrolysis and surface phosphonation, able to efficiently catalyze the synthesis of quinoxalines from 1,2-diamines and -hydroxi ketones, under aerobic conditions. The obtained results indicate that the type and number of acid sites drive the reaction in terms of conversion and selectivity. Furthermore, our experimental and theoretical observations suggest that the preferred reaction pathway for this transformation, in the presence of the investigated acid carbon catalysts, involves cascade reactions including imination reaction between reactants, successive imine-enamine and ceto-enol tautomerisms, heterocyclization followed by dehydration, and aromatization. While the acid sites seem to be a relevant role in each reaction step, the system formed by activated carbon and molecular oxygen could be behind the last oxidative reaction to give quinoxalines.