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-beta-carboline using an iron-mediated [2+2+1] cycloaddition as the key-step. Oxidation of (+/-)-demethoxycarbonyldihydrogambirtannine led to norketoyobyrine. (C) 2000 Elsevier Science Ltd. All rights reserved.