Chemoselective N-H or C-2 Arylation of Indole-2-carboxamides: Controllable Synthesis of Indolo[1,2- a]quinoxalin-6-ones and 2,3'-Spirobi[indolin]-2'-ones

Abstract

Novel methods involving the chemoselective N-H or C-2 arylation for the synthesis of indolo[1,2- a]quinoxalin-6-ones and 2,3'-spirobi[indolin]-2'-ones starting from indole-2-carboxamides were developed. When reactions were carried out using ZnI₂ as catalyst and Ag₂CO₃ as oxidant, indolo[1,2- a]quinoxalin-6-ones were synthesized in up to 86% yields via intramolecular N-H/C-H coupling, whereas the dearomative cyclization reactions were realized in the presence of TfOH, resulting in C-2 arylation of indole through C-H functionalization or a Fridel-Crafts alkylation reaction to give 2,3'-spirobi[indolin]-2'-ones in moderate to excellent yields.