Ethyl 1-benzyl-2-(4-methylphenyl)-1h-pyrrolo[2,3-b]quinoxaline-3-carboxylate and ethyl 6,7-dimethyl-1,2- diphenyl-1h-pyrrolo[2,3-b]quinoxaline-3-carboxylate: synthesis and study on nuclear magnetic resonance spectroscopy

Synthetic pyrrolo[2,3-b]quinoxalines have been confirmed to possess valuable biological activities and pharmacokinetic properties. However, the presence of heavy metal catalysts in synthesizing these heterocycles has restricted the application of those methods in pharmaceutical manufacturing. In this study, two pyrrolo[2,3-b]quinoxalines have been synthesized via the nucleophilic addition reaction between 1,5-disubstituted-4-ethoxycarbonyl-3-hydroxy-3-pyrrolin-2-ones and o-phenylenediamine or 4,5-dimethyl-o-phenylenediamine as nucleophiles in glacial acetic acid. In the acidic medium of acetic acid, 1,5-disubstituted-4-ethoxycarbonyl-3-hydroxy-3-pyrroline-2-ones could be tautomerized to keto tautomers, also known as 2,3-dioxopyrrolidine derivatives. More importantly, the structure of two desired pyrrolo[2,3-b]quinoxalines has been approved via nuclear magnetic resonance spectroscopy (1D NMR, 2D NMR) and high-resolution mass spectrometry (HRMS).