Adventures and Detours in the Synthesis of Hydropentalenes

Functionalized hydropentalenes (i.e., bicyclo[3.3.0]octanones) constitute important building blocks for natural products and for ligands for asymmetric catalysis. The assembly and tailored functionalization of this convex roof-shaped scaffold is challenging and has motivated a variety of synthetic approaches including our own contributions, which will be presented in this account. 1 Introduction 2 Biosynthesis of Hydropentalenes 3 Hydropentalenes through the Pauson–Khand Reaction 4 Hydropentalenes through Transannular Oxidative Cyclization of Cycloocta-1,4-diene 5 Functionalization of Bicyclo[3.3.0]octan-1,4-dione to Dodecahydrocyclopenta[a]indenes 6 Functionalization of Bicyclo[3.3.0]octan-1,4-diones to Crown Ether Hybrids 7 Functionalization of Bicyclo[3.3.0]octan-1,4-dione to Cylindramide 8 Tandem Ring-Opening Metathesis/Ring-Closing Metathesis/Cross-Metathesis of Bicyclo[2.2.1]heptanes 9 Functionalization of Bicyclo[3.3.0]octan-1,4-dione to Geodin A 10 Hydropentalenes through Enantioselective Desymmetrization of Weiss Diketones 11 Functionalization of Weiss Diketones by Carbonyl Ene Reactions 12 Functionalization of the Weiss Diketone to Cylindramide and Geodin A Core Units 13 Biological Properties of Bicyclo[3.3.0]octanes 14 Hydropentalenes through Vinylcyclopropane Cyclopentene Rearrangement 15 Functionalization of Bicyclo[3.3.0]octanes toward Chiral Dienes 16 Miscellaneous Syntheses of Hydropentalenes 17 Conclusion and Outlook