Synthesis of the 6,6,5,7-tetracyclic core of daphnilongeranin B.

An efficient approach toward the synthesis of the 6,6,5,7-tetracyclic core of the daphnilongeranin B, a Daphniphyllum alkaloid, is reported. The bridged 6,6-bicyclic system was constructed using a gold(I) catalysed Conia-ene reaction, while the 5-and 7-membered rings were assembled by two diastereoselective Michael addition reactions, respectively.