Stereoselective "pinacol" coupling of 2,3-O-isopropylidene-D- glyceraldehyde

The use of carbohydrate-derived aldehydes as building blocks for stereoselective synthesis of polyhydroxylated alkyl moieties can be an important alternative to other methods which might involve sequential linking of hydroxymethylene units. Pinacol coupling of sugar-derived aldehydes represents one such general, alternative methodology. The stereoselectivity of pinacol coupling observed for this simple carbohydrate suggests that similar procedures might be applicable for efficient preparation of higher carbohydrate derivatives, for use in synthesis of end products with interesting biological properties. The low rate of reactivity of 4 compared with 1 and the consequently higher temperature required to effect pinacol coupling with attendant lower coupling stereoselectivity suggest that, as for alkyl halide activation, dissociation of 4 to 3, or the creation of a vacant site by dissociation of a chloride ligand, might be rate determining for pinacol coupling, overall.