Synthesis of 4-hydroxy-2,6-bis(hydroxymethyl)tetrahydropyran-2-carbaldehyde derivatives

Cycloaddition of 1,3-dibromo-2-oxyallyl cation to 2-(benzyloxymethyl)furan provided a 8-oxabicyclo[3.2.1]hept-6-en-3-one derivative that was transformed into (2RS,3SR,4SR,5SR,6SR)-3,4-dibromo-2-benzyloxymethyl-2,6-bis(hydroxymethy l)-4- (methoxymethyloxy)tetrahydropyran. Selective protection and oxidation produced a protected 3,5-dibromo-4-hydroxy-2,6-bis(hydroxymethyl)tetrahydropyran-2-carbaldehy de that could be used to carry out cross-aldolisations, opening an approach to the synthesis of C-disaccharide analogues mimicking sialic acid glycosides