Total Syntheses of Aromatic Abietane Diterpenoids Utilizing Advances in the Pummerer Rearrangement.

The first total syntheses of triptobenzene T, vitexifolin C, 4- epi-triptobenzene L, triptobenzene L, and nepetaefolin F have been accomplished through an enantioselective, common intermediate approach and have enabled the confirmation and/or establishment of the absolute stereochemistry of each natural product synthesized. Application of three new and/or underutilized Pummerer reaction pathways proved critical to the synthetic work. A proline sulfonamide-catalyzed Yamada-Otani reaction was used to access the highly functionalized cyclohexane A ring core, including the C10 all-carbon quaternary stereocenter. Additionally, the importance of the A ring unsaturation for controlling the stereoselectivity during the C4 alkylation is showcased.