Enantioselective Total Synthesis of (−)-Arcutinine

The first total synthesis of an arcutine-type C₂₀-diterpenoid alkaloid arcutinine has been achieved in both racemic and asymmetric forms. Construction of the C4 quaternary center and the pyrrolidine E ring in an early stage proved to be important for achieving the successful synthesis of the target alkaloid. Strategically, an asymmetric conjugate addition/aldol cascade and a decarboxylative allylation reaction allowed the establishment of the vicinal all-carbon quaternary stereocenters at C4 and C5. Furthermore, a sequence consisting of an intramolecular aza-Wacker cyclization, an oxidative dearomatization/intramolecular Diels–Alder cycloaddition cascade, and a ketyl-olefin cyclization enabled the assembly of the core structure and led to the total synthesis of arcutinine.