Total Synthesis of Indole and Dihydroindole Alkaloids. VIII. Studies on the synthesis of bisindole alkaloids in the vinblastine‐vincristine series. The chloroindolenine approach

Studies on the syntheses of 18′‐epi‐4′‐deoxo‐4′‐epivinblastine (IX, R = CO 2 CH 3 ; R 1 = H), 18′‐decarbomethoxy‐18′‐epi‐4′‐deoxo‐4′‐epivinblastine (IX, R = R 1 = H) and related analogues are described. The synthetic method employs a coupling reaction involving chloroindolenine derivatives of the cleavamine series (for example, III) with vindoline (V) under acidic conditions. The complete structures, including absolute configuration, of the resulting dimers are established by a combination of chemical and spectroscopic techniques, including X‐ray analysis.