Trichloro-oxazolines as activated donors for aminosugar coupling.

Starting from tri-O-acetyl-D-glucal, a combination of the Overman rearrangement and subsequent dihydroxylation produces a range of aminosugars. These can be activated by formation of the corresponding trichloro-oxazolines, which are excellent glycosyl donors as they form disaccharides with good (trans) stereoselectivity under mild conditions. Propagation of these trichloro-oxazolines gave trisaccharides that can then be dehalogenated under a variety of conditions. [reaction: see text]