Glucofuranose derivatives rearrangement

Stereoselective rearrangement reactions can involve sugar-linked functionalities. An example of this type is the Overman rearrangement of allylic trichloracetimidates formed from a D-glucofuranose derivative 20 [36]. This methods affords (L)-a-ami-no acids 25 from (Z)-allylic imidate 23 and (R)-a-amino acids 25 from ( )-imidates 23 with a diastereoselectivity of about 16 1. The oxidative cleavage of compound 24 with Ru04 yields the a-amino acid 25, (Scheme 15). 

In these reactions to give derivatives of D-glucopyranosyl bromide, the original glucofuranose molecule has rearranged to the pyranose form, pre-... 

The rearrangement of a benzoxonium intermediate can be convincingly demonstrated in the reaction of 3,5-0-benzylidene-1,2-0-isopropylidene-a-D-glucofuranose (120) with N-bromosuccini-mide, whereby the 6-bromo derivative 124 and the 3,6-anhydride 123 are obtained. It may be presumed that the benzoxonium ion 121 rearranges into the ion 122 through intramolecular attack by... 

Dichlorocarbene (generated in situ from chloroform) reacted with l,2 5,6-di-0-isopropylidene-a-D-glucofuranose in a phase-transfer system to give the rearranged product 6-chloro-6-deoxy-l,2 3,5-di-0-isopropylidene-a-D-glucofuranose, whereas 2,3 5,6-di-O-isopropylidene-a-D-mannofuranosyl chloride was obtained from the reaction of dichlorocarbene with 2,3 5,6-di-0-isopropylidene-a-D-manno-furanose. The a-D-mannofuranosyl chloride derivative was used to prepare the corresponding methyl and benzyl a-glycofuranosides and in the synthesis of a-linked disaccharide derivatives. 

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