Asymmetric synthesis of epohelmins A, B and 3-epi ent-epohelmin A

An efficient method for asymmetric synthesis of epohelmins A (3), B (4) and their isomer 24 is detailed in this report. The key feature in this divergent synthesis includes the SmI2-induced cross-coupling of N-tert-butanesulfinyl imine 10 with chiral aldehyde 9 derived from d-malic acid. A cascade cyclization to the pyrrolizidine skeleton is achieved in our synthetic route for epohelmins. In addition, an interesting intramolecular oxa-Michael addition was observed for epohelmin A (3).

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