Synthesis of quinazolinones via radical cyclization of α-azidyl benzamides

This paper reports a new radical-based method for the synthesis of quinazolinones from α-azidyl benzamides. Under the conditions of visible light irradiation with N-bromosuccinimide (NBS), α-azidyl benzamides were transformed into the corresponding iminyl radicals via regio-selective α-hydrogen abstraction and denitrogenation; the thus formed iminyl radicals then underwent cyclization to afford the quinazolinones. The scope of this method was examined by applying it to α-azidyl benzamides of different structural features. It was found that the key cyclization step is influenced by conformational effects as well as substituent effects. As the current approach can be implemented under mild tin-free conditions by using readily accessible precursors, it has practical applicability in the synthesis of quinazolinones.