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 AlCl3 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. An efficient tandem process for the selective synthesis of 1,2‐annulated α‐fused quinoxalines using benzotriazole methodology by modified Pictet–Spengler reaction is described. This approach also provides a novel tandem synthesis of ring‐fused quinoxalinones.