Functionalization of the Anomeric C–H Bond of Carbohydrates: Old Strategies and New Opportunities

Abstract

After a quick review of the existing methods that enable the quaternarization of the anomeric position of carbohydrates via a C–H bond functionalization process, we summarize recent contributions from our group related to the preparation of α- and β-ketopyranosides by the 1,5-insertion of metal carbenes. 1 Introduction 2 Early Developments: Anchoring of Reactive Species at the Anomeric Position 2.1 Radical-Promoted Quaternarization of the Anomeric Position 2.2 Photochemically Induced Quaternarization of the Anomeric Position 2.3 Alkylidene-Promoted Quaternarization of the Anomeric Position 2.4 Nitrene-Promoted Quaternarization of the Anomeric Position 2.5 Any Possible Extension to the Preparation of α- and β-Ketopyranosides? 3 Carbene-Mediated Functionalization of the Anomeric C–H Bond of Carbohydrates 3.1 Functionalization of Carbohydrate Scaffolds by the Insertion of Metal Carbenes: A Challenging Task 3.2 Preparation of Carbene Precursors 3.3 Transition Metal Catalyzed Decomposition of Diazo Sugars 3.4 Dramatic Effects of Molecular Sieves 3.5 Ring Opening of γ-Lactones 4 Development of a Stereoselective Glycosylation/Diazo Transfer/Quaternarization Sequence 4.1 Preliminary Studies with a Permethylated Acceptor 4.2 Stereoselective Access to Quaternary Disaccharides: Scope and Limitations 5 Concluding Remarks