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.