Stereospecific Synthesis of 1,2-cis Glycosides by Allyl-Mediated Intramolecular Aglycon Delivery. 2. The Use of Glycosyl Fluorides

摘要

Stereospecific 1,2-cis glycosylation of 2-O-allyl-protected glucosyl and mannosyl fluorides via a sequence of allyl isomerization, N-iodosuccinimide-mediated techering, and intramolecular aglycon delivery (IAD) is reported. The use of fluoride as anomeric leaving group is advantageous is 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#-mannoosides in an entirely stereoselective manner.