Biomimetic Collective Total Synthesis of Bioactive Carbazole Alkaloids Indizoline, Mafaicheenamine A, Claulamine A, Claulansine A, and the Proposed Claulamine E

The
common precursor 1-methoxy-2-prenyl-3-carbomethoxycarbazole
was synthesized from dimethyl indolylmethylenesuccinate in four steps.
Well-planned reductive and/or oxidative transformations and intramolecular
cyclizations were performed on a pivotal common precursor to accomplish
collective first total synthesis of titled natural products and proposed
claulamine E. Burgess reagent induced formation of kinetically controlled
product claulamine A, and intramolecular cyclizations to form bicyclic
claulansine A were the key reactions. An alternatively attempted synthesis
failed to provide the structural isomer of proposed claulamine E.