Synthesis of Pentacyclic Core Structure ofAspidospermaAlkaloids by Sequential Ring Construction via Oxidative Phenolic Coupling

The common pentacyclic core structure of Aspidosperma alkaloids was assembled by means of a sequential ring construction strategy. The B ring was constructed by oxidative phenolic coupling reaction of diaryl amine using a hypervalent iodine reagent developed by our group, followed by intramolecular regioselective aza-Michael reaction of the resulting dienone to form the E ring. Then 6-exo-trig radical cyclization with V-601 as a radical initiator afforded the D ring with an all-carbon quaternary stereogenic center at C20. The common pentacyclic core structure of Aspidosperma alkaloids was assembled by means of a sequential ring construction strategy. The B and E rings were constructed by oxidative phenolic coupling reaction of diaryl amine using a hypervalent iodine reagent, followed by intramolecular regioselective aza-Michael reaction of the resulting dienone. Finally, 6-exo-trig radical cyclization afforded the D ring with an all-carbon quaternary stereogenic center at C20.