Palladium-Catalyzed Synthesis of Pyrayaquinones, Murrayaquinones, and Murrayafoline-B

Abstract

We describe the total synthesis of murrayafoline-B and seven carbazole-1,4-quinone alkaloids. A palladium(II)-catalyzed oxidative cyclization is used to construct the carbazole skeleton. Pyran annulation and oxidation provide pyrayaquinone-A, -B, and -C. DIBAL-H-promoted reductive ring opening of pyrano[3,2-<i>a</i>]carbazole precursors leads to the prenylated and geranylated carbazole-1,4-quinone alkaloids murrayaquinone-B, -C, -D, and -E and to murrayafoline-B.