Polyene Cyclization/Mannich Cascade for Streamlined Construction of the A/E/F Tricyclic System of Diterpenoid Alkaloids

The A/E/F tricyclic system characteristic of C₁₈-, C₁₉-, and denudatine-type C₂₀-diterpenoid alkaloids was constructed via a strategically designed polyene cyclization/Mannich cascade. The configurational inversion of the phenyl group at C7 successfully proceeded through a radical cascade process involving sequential 1,5-HAT and intermolecular HAT, ultimately establishing the desired tricyclic system with an β-oriented phenyl group.