Expedient entry into 1,4-dihydroquinoxalines and Quinoxalines via a novel variant of isocyanide-based MCR

A novel multicomponent reaction of o-phenylenediamines with aldehydes and isonitriles yields 1,4-dihydroquinoxalines. These intermediates are unstable under reaction conditions. They undergo oxidation with DDQ to furnish 33-54% isolated yields of the respective quinoxalines. This reaction is general for aromatic 1,2-diamines. Monoalkylated aryl 1,2-diamines lead to stable 1,4-dihydroquinoxalines.