A Unified Strategy to Construct the Tetracyclic Ring of Calyciphylline A Alkaloids: Total Synthesis of Himalensine A

The synthetic approach to the core framework of the calyciphylline A-type Daphniphyllum alkaloids and total synthesis of himalensine A were described herein. Nitrone-induced 1,3-dipolar [3 + 2] cycloaddition was applied for the construction of A/C rings along with the all-carbon quaternary center. Pd-catalyzed enolate alkenylation and ring closing metathesis (RCM) were adopted to install the B/D rings to accomplish the [6,6,5,7] core framework. Nazarov reaction was utilized to install the F ring to complete the total synthesis of himalensine A.