2 - Selective Hydroxyl Protection and Deprotection

Abstract

Ensuring that a particular functional group undergoes reaction without interference from others can be achieved by blocking the others with protecting groups. Carbohydrates present particular problems as they possess a number of nucleophilic and mildly acidic hydroxyl groups arranged on relatively short carbon chains, and the density of functionality is accordingly high. In general, the various hydroxyl groups cannot be considered in isolation; their reactivity influences, and is influenced by, neighbouring functionality. Any modifications made to one of them often leads to changes in the relative reactivity of the others. Because of these subtleties, carbohydrate chemistry may appear to have a large associated lore, which can seem unnecessarily arcane to the uninitiated. In the past, this has led to a separation of carbohydrate chemistry from what was regarded as mainstream organic synthesis. A steady integration of the field that now occupies a central position within organic synthesis has led to increased control of carbohydrate reactivity, not only in the traditional areas of monosaccharide and oligosaccharide synthesis, but also for the preparation of carbohydrate mimics such as C-glycosides and imino sugars, and in the synthesis of glycosylated natural products and intermediates for non-carbohydrate compounds.