Synthesis of benzo-γ-carboline alkaloid cryptosanginolentine by reaction of indole-2,3-dicarboxylic anhydrides with anilines

1-Benzenesulfonylindole-2,3-dicarboxylic anhydride was reacted with aniline to give the 2-carbamoylindole-3-carboxylic acid as the sole product, but with N-methylaniline, the 3-carbamoylindole-2-carboxylic acid was the major product, which could be transformed into the 1-benzenesulfonylbenzo-γ-carbolinone in the presence of Pd(OCOCF3)2. The reduction of the benzo-γ-carbolinone with LiAlH4 gave the cryptosanginolentine in high yield.