Two-Step Total Syntheses of Canthin-6-one Alkaloids: New One-Pot Sequential Pd-Catalyzed Suzuki−Miyaura Coupling and Cu-Catalyzed Amidation Reaction

Canthin-6-one (1) and nine analogues including the naturally occurring 9-methoxycanthin-6-one (2) and amaroridine (3) are prepared rapidly and in high yields via a convergent "non-classical" strategy that focuses on construction of the central ring B. The strategy relies on concomitant Pd-catalyzed Suzuki-Miyaura C-C coupling followed by a Cu-catalyzed C-N coupling that can be achieved either stepwise or in a new one-pot protocol starting from the appropriate 8-bromo-1,5-naphthyridine.