An alternative synthesis of 10H-indolo[3,2-b]quinoline and its selective N-alkylation

A new and a more efficient synthesis of 10H-Indolo[3,2-b]quinoline (quindoline) is reported. The synthesis involved N-arylation of 3-aminoquinoline with triphenylbismuth diacetate followed by oxidative cyclization using palladium(II) acetate. A selective N-alkylation methodology for quindoline was also developed. Alkylation on N-5 was obtained in sulpholane, while alkylation on N-10 was achieved in acetone in the presence of potassium hydroxide. A sequential N-5- and N-10 double alkylation procedure was also formulated.