Selective Synthesis of 1,2-cis-α-Glycosides without Directing Groups. Application to Iterative Oligosaccharide Synthesis

A method for the highly selective synthesis of 1,2-cis-alpha-linked glycosides that does not require the use of the specialized protecting group patterns normally employed to control diastereoselectivity is described. Thioglycoside acceptors can be used, permitting iterative oligosaccharide synthesis. The approach eliminates the need for lengthy syntheses of monosaccharides possessing highly specialized and unconventional protecting group patterns.