Microwave-assisted Iodine-catalyzed Rapid Synthesis of 6H-indolo[2,3-b] quinolines: Formal Synthesis of Cryptotackieine

Background: Indoloquinoline alkaloids are of great importance due to their unique structure and various biological activities. Several methods have been developed to synthesize indoloquinolines and among those, one-pot methods are of particular importance due to its simplified reaction procedure. Methods: We investigated the one-pot reaction of indole-3-carboxyaldehyde and aniline in presence of catalytic amount of I2 in automated microwave. Results: An efficient microwave-mediated tandem synthesis of several linear indoloquinoline alkaloids using 10 mol% iodine as catalyst under mild reaction conditions is described. The reaction involved key steps of imination / nucleophilic addition / annulation / aromatization, all in one pot, in a highly efficient manner under microwave irradiation. Conclusion: We have developed an extremely rapid and convenient microwave-assisted method for the synthesis of important class of indoloquinolines using environmentally benign I2 as catalyst in one-pot.