Alkylated disaccharides

Mesoporous aluminosilicates are of special interest as catalysts for the alkylation of ketoses, which are prone to degradation when treated with strong acid catalysts. Although disaccharides are generally subject to alcoholysis under strong acid catalysis, the use of MCM-41 as acid catalyst enables the selective preparation of alkylated disaccharides in good yield. 

Simple alkyl carbonates have also been used as glycosyl donors with the addition of an external glycosyl acceptor. Sinay and coworkers have reported that 2-propenyl carbonate donors, such as 151 (R = 2-propenyl), are activated with TMSOTf at —25 °C to afford good yields of disaccharide products [358]. Disaccharide... 

Anomeric alkylation has been extensively studied by Schmidt and co-workers,62 and the main alkylating agents used were dialkyl sulphates, benzyl bromide, allyl bromide63 or various O-triflates, allowing the synthesis of disaccharides.64 The stereochemical outcome of anomeric alkylation is known to depend on many parameters such as the base, the solvent and its effect on solubility and concentration, the temperature, chelation effects, presence of additives, and nature of the electrophilic species.62 65... 

The enolic double bond of a difluorovinyl group in the anomeric position is able to add a radical. It can thus afford a difluoro-C-glycoside, either directly or indirectly. When the alkylating radical is generated from a 6-halogenopyranoside, the reaction can lead to difluoro-C-disaccharide. These reactions are even more efficient if the radical has an electrophilic character (e.g., with an a-halogenoester instead of an alkyl radical). 

The D-mannose subunit 23 (Scheme 5) was prepared from D-mannose itself. This was designed to use an acetate at C2 to control the stereochemistry of the disaccharide glycosyl-ation reaction. The precursor 22 was obtained by exclusive alkylation of the equatorial C3 alcohol. 

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