Due to the profound extent to which natural products inspire medicinal chemists in drug discovery, there is demand for innovative syntheses of these often complex materials. This article describes the synthesis of tricarbocyclic natural product architectures through an extension of the enantioselective Birch-Cope sequence with intramolecular Friedel-Crafts alkylation reactions. Additionally, palladium-catalyzed enol silane cycloalkenylation of the tricarbocyclic structures afforded the challenging bicyclo[3.2.1]octane C/D ring system found in the gibberellins and the ent-kauranes, two natural products with diverse medicinal value. In the case of the ent-kaurane derivative, an unprecedented alkene rearrangement converted four alkene isomers to one final product.

Reactions. -Tricarbocyclic products (II) are obtained by an extension of the enantioselective Birch-Cope sequence with Friedel-Crafts alkylation reactions. Furthermore, the bicyclo[3.2.1]octanes are constructed by palladium-catalyzed enol silane cycloalkenylation of the tricyclic structures. -(BURKE, S. J.; MALACHOWSKI*, W. P.; MEHTA, S. K.; APPENTENG, R.; Org. Biomol. Chem. 13 (2015) 9, 2726-2744, http://dx.doi.org/10.1039/C4OB02489C ; Dep. Chem., Bryn Mawr Coll., Bryn Mawr, PA 19010, USA; Eng.) -H. Toeppel