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Lifetime of the glucosyl oxocarbenium ion and stereoselectivity in the glycosidation of phenols with 1,2-anhydro-3,4,6-tri-O-methyl-α-d-glucopyranose

✍ Scribed by Cinzia Chiappe; Giacomo Lo Moro; Paola Munforte

Publisher
Elsevier Science
Year
1997
Tongue
French
Weight
522 KB
Volume
53
Category
Article
ISSN
0040-4020

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✦ Synopsis

The glycosidation of para substitued phenols with 1,2-anhydro-3,4,6-tri-O-methyl-et-Dglucopyranose. ZnCI 2 catalyzed, gives predominatly the corresponding Gt-anomers. In the presence of an amino base, 1.1,3,3-tetramethylguanidine. however, enhances the I~-selectivity, which becomes practically complete when the reaction is carried out under basic conditions, by addition of K2CO 3 and 18-crown-6. A rationaliation based on the lifetime of the oxocarbenium ion intermediate and on the nucleophilicity of the phenols is proposed.

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