Stereocontrolled Assembly of Cis or Trans Angularly Substituted Hydrindenes by the Unactivated Intramolecular Diels-Alder Reaction.

The unactivated intramolecular Diels-Alder reaction has become a powerful tool for the construction of polycyclic natural products. Nevertheless, the factors that govern diastereoselectivity in these cyclizations have not been fully understood. We here report that through the choice of the proper substituents, it is possible to make the unactivated intramolecular Diels-Alder reaction proceed to give either the cis angularly-substituted hydrindene 12b or the trans product 19a.