Studies on the Alkaloids of Menispermaceous Plants. CCXLII. Synthesis of Cycleanine. (3). Synthesis of dl-Cycleanine

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The cyclobisamide IV was synthesized by intramolecular condensation of an ω-amino acid XIII or its corresponding p-nitrophenyl ester. Bischler-Napieralski cyclization of IV followed by NaBH₄ reduction and N-methylation gave a mixture of N-methyltetrahydroisoquinolines, from which dl-cycleanine (XIV), the diastereoisomer of cycleanine (XV), and a structural isomer of cycleanine (XVII) were isolated in crystalline state. The structural elucidations of the products were effected by IR, NMR, and mass spectral comparisons with the natural base. The structure of the isomeric product XVII was further proved by sodium-liquid ammonia cleavage reaction which afforded XVIII as the bisected product.