Stereospecific synthesis of 1,2-cis glycosides by allyl-mediated intramolecular aglycon delivery.: 2.: The use of glycosyl fluorides

[GRAPHICS] Stereospecific 1,2-cis glycosylation of 2-O-allyl-protected glucosyl and mannosyl fluorides via a sequence of allyl isomerization, N-iodosuccinimide-mediated tethering, and intramolecular aglycon delivery (IAD) is reported, The use of fluoride as anomeric leaving group is advantageous in that tethering efficiencies can be increased for hindered aglycon alcohols by the use of extended reaction times without competitive anomeric activation, Intramolecular glycosylation furnishes the desired alpha -glucosides and beta -mannosides in an entirely stereoselective manner.