Total synthesis of ent-(+)-cinanthrenol A.

The first total synthesis of ent-(+)-cinanthrenol A of potent estrogenic activity was achieved with 10.9% overall yield in 13 steps from commercially available materials. Our synthesis features a photo-promoted oxidative 6π-electron electrocyclization/aromatization for construction of the cyclopenta[a]phenanthren-17-one and Furukawa hydroxyl-directed cyclopropanation for the rare spiro[2,4]heptane. The brevity of this synthetic strategy would allow an expedited access to cinanthrenol A and its analogs for further biological evaluation.