Strategies for Spiroketal Synthesis Based on Transition-Metal Catalysis

The transition-metal-catalyzed synthesis of spiroketals is a rapidly growing area and these methods have facilitated the use of new spiroketal synthons as latent spiroketal equivalents. This review highlights the different substrate classes and provides select examples of applications in natural product synthesis. 1 Introduction 2 Conformational Aspects of Spiroketal Structures 3 Traditional Approaches to Spiroketal Synthesis 4 Transition-Metal-Catalyzed Spiroketalization 4.1 Dihydroalkoxylation of Alkynediols 4.2 Spiroketalization of Monopropargylic Triols 4.3 Intramolecular Reaction of Epoxy Alkynes 4.4 Spiroketalization of Propargyl Vinyl Ethers 4.5 Oxycarbonylation of Dienones 4.6 Transposition of Allylic Alcohols 4.7 Hetero-Diels-Alder Reaction 4.8 Cyclization of Monoacetylated Ketodiol 4.9 Ring-Rearrangement and Ring-Closing Metathesis 4.10 [2+2+2] Cycloaddition of C-Alkynyl Carbohydrates 4.11 Pauson-Khand Reaction of Ketal Enynes 4.12 Tandem Cyclization and Cross-Coupling Reactions of beta-Bromoketals and Aryl Iodides 4.13 Applications to Natural Product Synthesis 5 Outlook