A concise synthesis of indoloquinoline skeletons applying two consecutive Pd-catalyzed reactions

The indoloquinoline alkaloids cryptolepine (1), neocryptolepine (2), isocryptolepine (3), and isoneocryptolepine (4) are important tools in traditional medicine. Now, their precursors 1a-4a were synthesized in two steps starting from the corresponding bromo-iodoquinolines. Our strategy is based on palladium-catalyzed reactions, applying regioselective Buchwald-Hartwig amination on 2,3- and 3,4-dihaloquinolines followed by an intramolecular Heck-type reaction. Both steps were carried out under microwave irradiation.