Improved iterative olefination approach to oligosaccharide mimics: stereoselective synthesis of β-(1→6)-d-galactopentaose methylene isostere

The title C-pentagalactoside featuring β-(1→6) ethylene bridges between the d-galactopyranose units has been prepared through four consecutive cycles comprising the Wittig reaction of a formyl C-galactoside building block with sugar phosphorane substrate followed by the introduction of a methylphosphonium group at the nonreducing end; the target product was obtained by hydrogenolysis of the tetraene pentasaccharide.