Synthesis of a Halicyclamine-Type Macrocyclic Scaffold via Biomimetic Transannular Cyclization

Previous attempts for biomimetic transannular reactions between two dihydropyrdine (DHP) rings incorporated in macrocycle frameworks relevant to manzamine alkaloids have been unsuccessful. Herein, we report an efficient regiocontrolled transannular cyclization of C 2-symmetric macrocyclic precursor with rational modifications of the 3 and 6 positions of the DHP rings to synthesize a halicyclamine-type scaffold. The cis-double bonds installed in the macrocyclic alkyl loops played a crucial role in achieving the biomimetic transannular cyclization.