O-Glycosidation of phenols

T. Matsumoto, M. Katsuki, and K. Suzuki, Rapid O-glycosidation of phenols with glycosyl fluoride by using the combinational activator, Cp2HfCl2 and AgC104, Chem. Lett., p. 437 (1989). 

O-Glycosidation of phenols.3 O-Aryl glycosides can be obtained in high yield by reaction of glycosyl fluorides with phenols in the presence of 4-A MS and this activator system. This hafnium complex is superior to Cp2ZrCl2, which is more useful for glycosidation of alcohols. 

C. Chiappe, G. L. Moro, and P. Munforte, Lifetime of the glucosyl oxocarbenium ion and stereoselectivity in the glycosidation of phenols with 1,2-anhydro-3,4,6-tri-O-mcthyl-u-D-glucopyranose, Tetrahedron, 53 (1997) 10471-10478. 

Because direct glycosidation of 4 with phenols is not possible, indirect methods must be used for the preparation of aryl D-glucofuranosidurono-6,3-lactones (29). In addition, aryl 2,5-di-O-acetyl-D-glucofuranosidurono-6,3-lactones (30), obtained35-37 from the reaction of 1,2,5-tri-0-acetyl-D-glucofuranurono-6,3-lactones with phenols, can only be deacetylated by such multi-step procedures as (1) ammonolysis of 30 to afford aryl D-glucofuranosiduronamides (31), followed by amide hydrolysis and lactonization, 35,37 or (2) reduction of 30 with lithium aluminum hydride, and subsequent oxidation of the intermediate aryl D-glucofuranosides38 (32) (see Scheme 1). 

The glycosylation based on the Mitsunobu reaction has been most commonly directed to the synthesis of O-aryl glycosides, a structural motif found in a variety of natural products [80-82], Early work by Grynkiewicz [83,84], among others [85-87], established the viability of triphenylphosphine and diethylazodicarboxylate to promote the glycosylation of phenol acceptors at ambient temperature. More recently, Roush and coworkers have discovered that the glycosylation performed well in the... 

Akunzemann, J. and Herrmann, K. (1977) Isolation and identification of flavon (ol)-O-glycosides in caraway (Carum carvi), fennel (Foeniculum vulgare Mill.), anise (Pimpinella anisum L.) and coriander (Coriandrum sativum L.) and of flavone-C-glycosides in anise. I. Phenolics of spices. Z Lebensm Unters Forsch 164, 194-200. 

O-Glycosides occur in immense variety with glucose and other sugars being joined to the OH groups of alcohols and phenols to form acetals. The stereochemistry of these compounds is usually described by the Greek letters a and If the OR bond is down, we have an a-glycoside if up, a (5-gly coside. 

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