An approach to the synthesis of α-(1-6)-C-disaccharides by tandem Tebbe methylenation and Claisen rearrangement

Uronic acids, most efficiently synthesised from the corresponding alcohols by two step Dess-Martin and sodium chlorite mediated oxidation, may be used as coupling partners for esterification with an allo glycal as substrates for the tandem Tebbe/Claisen approach to the synthesis of 1-6 linked C-disaccharides. Whilst esters of glucuronic and mannuronic acids successfully undergo Tebbe methylenation, esters derived from galacturonic acids are unreactive under these conditions. Thermal Claisen rearrangement of vinyl ethers produced by methylenation yields α-C-disaccharides with complete control of anomeric stereochemistry.