Enantioselective route to an AE-ring intermediate in the total synthesis of talatisamine

Talatisamine [(–)-1] is a C19-diterpenoid alkaloid with an intricately fused ABCDEF-ring system. In 2020, we reported a total synthesis of racemic talatisamine [(±)-1], in which AE-ring fragment (±)-5-α/5-β was utilized as the pivotal early-stage intermediate. Herein, we disclose the development of an enantioselective route to (–)-5-β for the total synthesis of (–)-1. Enantioselective intermolecular Mannich, Lewis acid-mediated intramolecular Mannich, and reductive N-ethylation reactions were employed as the three key transformations.