Mannich biscyclizations. Total synthesis of (-)-ajmalicine

Article abstract of DOI:10.1021/ja00141a004

A concise enantioselective total synthesis of the cardiovascular agent (-)-ajmalicine and an approach toward the synthesis of (+)-19-epiajmalicine are described. The key step of the (-)-ajmalicine synthesis is a carboxylate-terminated N-acyliminium ion biscyclization (74 → 67), which assembles the D and E rings of this heteroyohimbine alkaloid in one step. A related carboxylate-terminated iminium ion biscyclization (28 → 29) is the central step in the approach to (+)-epiajmalicine.