Recent Developments in the Synthesis of 2,3-dideoxy-hex-2-enopyranosides: A Review

Abstract

2,3-Dideoxy-hex-2-enopyranosides, also described as 2,3-unsaturated glycosides, constitute an important class of carbohydrate derivatives because their double bond and anomeric substituent enable diverse synthetic transformations. This review summarises recent developments in the preparation and application of O-, P-, C-, N-, S- and Se-2,3-unsaturated glycosides, with emphasis on the principal synthetic routes, catalysts and reaction outcomes described in the manuscript. Particular attention is given to the Ferrier rearrangement, which remains the most widely applied strategy for converting glycals into 2,3-unsaturated glycosyl derivatives using Lewis acid or related catalytic systems. Other routes, including the Fraser-Reid and Boctor method, the Zamojski and Achmatowicz approach, Tebbe methylenation/Claisen rearrangement and Heck coupling, are also considered as complementary procedures for constructing these scaffolds. The review further discusses the reactivity of unsaturated glycosides as substrates for functionalisation reactions, including Overman rearrangement, Mitsunobu reaction, oxidation, catalytic hydrogenation, decarboxylative allylation, glycosylation of proteins and lipids, epoxidation, cycloaddition, hydrothiolation and allyl cyanate/isocyanate rearrangement. These transformations demonstrate the usefulness of the 2,3-olefinic moiety for accessing structurally varied carbohydrate derivatives and related building blocks. The manuscript also considers reported applications involving structural modification, stereochemical control and the preparation of biologically relevant carbohydrate frameworks, while avoiding extrapolation beyond the cited reactions. Recent perspectives on greener catalytic systems, metal-free methods and late-stage functionalisation are also outlined, together with limitations associated with stereochemical control, side reactions, functional group tolerance and catalyst requirements. Overall, the manuscript presents a focused account of advances in the synthesis and use of 2,3-dideoxy-hex-2-enopyranosides in carbohydrate chemistry and identifies areas where further methodological development may be beneficial.