Alkylation, Allenylation, Allylation and Alkynation Reactions

Although activating sugars is a common method to modify carbohydrate stmctures in preparation for further reactions, these changes generally retain the overall nature of the pyranose or furanose 

4 Lewis Acid-Mediated Couplings with Olefins 

Anionic nucleophiles provide valuable and versatile routes for the preparation of C-glycosides. However, the most extensively used technologies lie within the chemistry of Lewis acid-mediated reactions of carbohydrates with unsaturated hydrocarbons and derivatives thereof. In the next series of examples, reactions of sugars and sugar derivatives with olefins and their silyl-, stannyl-, and aluminum derivatives are discussed. 

In addition to glycosyl acetates, 1-O-trifluoroacetyl [79] and 1-O-p-nitrobenzoyl esters [68], trichloroacetimidates [2], methyl glycosides [80-83], furanose glycosyl acetates [48] and ketose acetates [84] have been successfully modified in this manner. With respect to the use of -0-p-nitrobenzoyl esters, extended olefins [85,86], substituted olefins [87] and allenes [88] were incorporated onto sugar scaffolds. 

Having addressed numerous activating groups compatible with the Lewis acid-mediated reaction with silyl-based reagents, we cannot ignore the utility of glycosyl fluorides, nitrates and glycals. This chemistry will be presented in the context of reactions with both allylsilanes and sUyl enol ethers. 

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