Tricyclo3.3.0.02,8octan‐3‐ones: Photochemically Prepared Building Blocks for Enantiospecific Total Syntheses of Cyclopentanoid Natural Products

Abstract Bi‐ and tricyclopentanoid natural products have been in the focus of synthetic interest in recent years. With widely applicable building blocks lacking, most work has been restricted in the past to specific approaches to single racemic target structures. A novel concept is now presented which uses for the first time a simple building block, tricyclo3.3.0.0 2,8 octan‐3‐one, providing enantiospecific access to diverse cyclopentanoid structures. Tricyclooctanone is obtained in a few steps and in high yield from benzene, via the triplet‐sensitized oxadi‐π‐methane rearrangement of bicyclo2.2.2octenone as a photochemical key reaction. Smooth preparations of both enantiomers are possible by resolving the racemic mixture and of the bicyclooctenone. Owing to its structural properties the tricyclooctanone undergoes a wide array of regio‐ and stereoselective transformations in high yields, in compliance with the expectations for a synthetic key compound of general applicability. The total syntheses of boschnialactone, allodolicholactone, irido‐ and isoiridomyrmecin, and loganin aglucone 6‐acetate provide the first examples of successful applications. Promising entries to coriolin, 6a‐carbaprostacyclin and homologs, and 6,11‐dehydroestrone complement this review of the potential of tricyclooctanone as a versatile building block for the enantiospecific total synthesis of polycyclopentanoids and related compounds.