An expeditious I2-catalyzed entry into 6H-indolo[2,3-b]quinoline system of cryptotackieine.

A synthesis of a series of novel 6H-indolo[2,3-b]quinolines with different substituents on the quinoline ring is described. The method involves reaction of indole-3-carboxyaldehyde with aryl amines in the presence of a catalytic amount of iodine in refluxing diphenyl ether to yield indolo[2,3-b]quinolines in one-pot. The present approach provides a new route for the synthesis of polycyclic structures related to an alkaloid cryptotackieine (neocryptolepine).