[reaction: see text] Thioglycosides of natural monosaccharides are readily converted into their corresponding chlorides by diphenylchlorosulfonium chloride. This reagent can likewise effect the conversion of the more stable 4-chlorophenylthio 2-deoxy-2-fluoroglucose derivatives into chloride glycosyl donors. On the basis of this activation strategy, it was possible to assemble unnatural oligosaccharides composed of 2-fluorodeoxy sugars.

The synthesis of 4,6-di-0-acetyl-3-0-(tetra-0-acetyl-B-D-galactopyranosyl)-2-deoxy-2-phthaiimido-a,B-D-galactopyranosyl chloride 1 4 and its 6-0 -benzyl derivative 1 2 was achieved in a 5-step sequence starting from the readily available type I disaccharide derivative 3.The key step in the synthesis involved the preparation of trifluoromethanesulfonate (triflate) derivatives 7 and 9 and their subsequent S N 2 displacement by acetate ion for conversion of 2-deoxy-2-phthalimido-G-D-glucopyranosyl moiety to the corresponding galacto configuration.

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