Concise Synthesis of the Oxapentacyclic Core of Cortistatin A

A concise synthetic approach for constructing the oxapentacyclic framework of cortistatin A is described. The synthesis features a furan−oxyallyl [4 + 3] cycloaddition and double-intramolecular aldol reactions. In addition, an interesting core structure was obtained in 11 steps from furan by using our method.