Enantioselective Total Synthesis of (+)-Pedrolide

The first total synthesis of (+)-pedrolide, a tigliane-derived diterpenoid featuring an unprecedented 5-5-6-6-3 carbon skeleton, is reported. Key to the approach is the construction of the bicyclo2.2.1heptane core via an intramolecular cyclopentadiene-Diels-Alder cycloaddition. To this end, a norbornadiene serves as an effective surrogate for cyclopentadiene, which is unmasked under mild conditions involving a complex Diels-Alder reaction cascade. In addition, the synthesis provides a novel approach to a densely functionalized carane in an efficient and enantioselective manner.