Lewis Acid‐Catalyzed Selective Synthesis of Diversely Substituted Indolo‐ and Pyrrolo[1,2‐a]quinoxalines and Quinoxalinones by Modified Pictet–Spengler Reaction

An efficient tandem process for the selective synthesis of 1,2‐annulated α‐fused quinoxalines using benzotriazole methodology by a modified Pictet–Spengler reaction is described. The approach involves the reaction of arylamines 4 with aromatic aldehydes 5 to furnish 6‐ endo‐dig ‐cyclized products. Dihydroquinoxalines 6 were selectively obtained by using AlCl 3 in tetrahydrofuran (THF) at room temperature for two hours. However, after ten hours, quinoxalines 7 were obtained exclusively in excellent yields. A series of biologically important fluoro‐ and piperazenyl‐substituted quinoxalines were also synthesized. This developed methodology also provides access to a novel tandem synthesis of quinoxalinones 9 .