Transition metal complexes in organic synthesis. Part 62: Total synthesis of (±)-demethoxycarbonyldihydrogambirtannine and norketoyobyrine by an iron-mediated [2+2+1] cycloaddition

(±)-Demethoxycarbonyldihydrogambirtannine was obtained in six steps and 49% overall yield from 3,4-dihydro-β-carboline using an iron-mediated [2+2+1] cycloaddition as the key-step. Oxidation of (±)-demethoxycarbonyldihydrogambirtannine led to norketoyobyrine.