A one-step C-linked disaccharide synthesis from carbohydrate allylsilanes and tri-O-acetyl-D-glucal

The reaction of protected glucuronic esters 2 and 7, as well as D-glucuronolactone derivative 11, with (trimethylsilyl)methylmagnesium chloride in ether led to the corresponding stable bis-silyl adducts 3, 8, and 12, respectively. In Peterson-type reactions catalysed with mild acid, these compounds yielded carbohydrate allylsilanes 4, 9, and 13, respectively. Synthons 4 and 9 were coupled with tri-O-acetyl-D-glucal in a boron trifluoride-catalysed "carbon-Ferrier rearrangement" reaction to give C-linked disaccharides i.e., so-called "C-disaccharides" 16 and 17, respectively, in fair yields. Structural assignments of the anomeric configuration at the C-glycosylic carbon in the 2,3-unsaturated ring of these coupling products with the aid of n.m.r. spectroscopic methods unambiguously showed that alpha-D-C-linked disaccharides had been formed.