I. Studies on the synthesis of iboga alkaloids. In the preliminary experiments for the total synthesis of ibogaine, the Schenker's isoquinuclidine synthesis was followed and modified in this laboratory. Thus, the new stereoisomer (VIb, m.p. 116-117°) was obtained, and its stereochemistry was clarified. The n.m.r. spectral data provided further information about the inversion of the substituent on the trivalent nitrogen of these compounds. Moreover, the epimerization of the compounds (Vb and VIIb) into VIb with a catalytic amount of t-BuOK in t-BaOH was extended to the similar conversion of Va into VIa, which was advantageous for the subsequent Ziegler condensation. And the total synthetis of C_<(21)^->-nor-20-hydroxylbogamine in the form of its racemate was achieved. In connection with this work, anhydrous (98-100) formic acid was found to be an effective catalyst for the Fischer indolization. II. The application of the Meerwein reagent (Et_3O^+BF_4^-) to the organic syntheses. The Meerwein reagent which is effective in preparation of the active iminoethers from the corresponding amides, was successfully applied to the oxindole derivatives. In the preliminary experiments, the steric factors have been shown to be very significant in the reactivities of the iminoethers obtained in this way. Thus, the compound (XIII) through XII was synthesized. This compound could be an important intermediate for syntheses of aspidosperma, iboga and strychnos alkaloids.
