A new route to ring-fused pyrazines: Imidazo[4,5-b]quinoxalines by a simple oxidation-annulation sequence

Abstract

Novel tricyclic 4H-imidazo[4,5-b]quinoxalines were synthesized by a new orfto-annulation process starting from 4Himidazoles and cerammonium nitrate (CAN) as oxidation reagent in the presence of potassium carbonate as base. This reaction is interpreted as a multi-step reaction involving oxidative radical formation, a radical aromatic substitution and a subsequent redox process. The analysis is supported by high level DFT calculations. This novel transformation opens the way for the construction of ring-fused derivatives of pyrazine. The new tricyclic products display strong fluorescence in solution and, in addition, show reversible redox activity.