Asymmetric Synthesis of the Pentacyclic Framework of Kopsia Alkaloids

Pyrroloazocine alkaloids from the Kopsia genus exhibit structural complexity and pharmacological potential. We report the concise and asymmetric synthesis of a pentacyclic core from l-proline. The key features include a C-N-C chirality transfer process to prepare the α-tertiary amine intermediate enantioselectively, an eight-membered C ring-forming Friedel-Crafts reaction at the indole C3 position, and a dearomative indole-Claisen rearrangement to form a bridged pentacyclic scaffold. This study provides a versatile platform for the divergent synthesis of diverse Kopsia alkaloids.