Sugars containing alpha,beta-unsaturated carbonyl systems: synthesis and their usefulness as scaffolds in carbohydrate chemistry.

The alpha,beta-unsaturated carbonyl function occurs in a wide variety of bioactive natural products. It is usually associated with the bioactivities of these compounds and acts as Michael acceptors for the addition of protein nucleophilic groups. The design and synthesis of sugars containing this functionality has provided a wide range of compounds, which can serve as building blocks of high synthetic versatility. This review deals with the chemistry of sugar-based molecules bearing singly linked or fused unsaturated lactones and ketones along with that of pyranoid enones and enonolactones. Examples are given of their syntheses and transformations into a variety of complex sugar derivatives such as branched-chain sugars, C-nucleosides, C-glycosyl derivatives, and various natural products, including selected analogues.