Glucopyranosyl chloride rearrangements

The unstable forms of the poly-O-acetylglycosyl halides, that is, those of the /3-series, have in many cases been obtained crystalline. They are characterized by their extremely easy rearrangement to the stable forms most of them, with the exception of the fluorides, undergo rearrangement when dissolved in polar solvents. Thus, tetra-O-acetyl-jS-D-glucopyranosyl chloride rearranges rapidly, even in pure chloroform. The mechanism of this rearrangement has been discussed by Hassel and Ottar and by Lemieux. ... 

In a study of the reaction of the anomeric forms of penta-O-acetyl-D-glucopyranose with titanium chloride in chloroform solution, Lemieux and Brice have found that, at 40°, the a-D anomer reacts but slowly, whereas the /3-d anomer reacts extremely rapidly, with the initial formation of (unstable) tetra-0-acetyl- S-D-glucopyranosyl chloride which then rearranges relatively slowly to (stable) tetra-O-acetyl-a-D-glucopyranosyl chloride. 

The Q- and -glycosidic products formed by reaction of tetra-Q-acetyl-a-D-glucopyranosyl chloride with various methoxy-substitutad phenylmagnesium bromides have been examined.That aryl Q-glycosides can rearrange to aryl -glycosides is illustrated in Scheme 21, and likewise the 9-naphthylglycoside CHjOMe... 

Octa-O-acetylcellobiose can, likewise, be rearranged by the action of corresponding excesses of aluminum trichloride and phosphorus pentachloride, and thereby gives the heptaacetate of 4-0-j3-d-glucopyranosyl-a-D-altropyranosyl chloride in 40-45% yield. Again, inversion at C-2 and C-3 of the reducing residue is observed. The formation of D-mannose and D-altrose derivatives is observed when penta-O-acetyl-D-glucopyranose is treated with aluminum trichloride-phosphorus pentachloride. ... 

Obtained (via O fi C glycoside rearrangement) by adding boron trifluoride etherate to a mixture of 2-(benzyloxy)-6-hydroxy-4-methoxy-acetophenone, 2,3,4,6-tetra-O-benzyl-a-D-glucopyranosyl fluoride (R) and powdered molecular sieves 4 A in methylene chloride and stirring at -78° for 2 h under an argon atmosphere after the disappearance of (R) on TLC, the reaction temperature was raised from -78° to r.t. and the mixture stirred for 45 min (78%) [3198]. 

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