Other Anomeric-Oxygen Activation Methods

Other Glycosyl Imidates, Glycosyl Carboxylates, and Glycosyl 

Acetimidate formation with A-methylacetamide and acylated glycosyl halides according to Sinay et al (212,213), using three equivalents of silver oxide as an activator, leads neither to particularly stable nor to reactive donors. Any other developments along these lines have already been summarized in previous reviews (1,3). The same is mainly true for anomeric 

The requirements for new glycosylation methods outlined at the beginning of this chapter, namely convenient diastereocontrolled anomeric O-ac-tivation (first step) and subsequent efficient diasterecontrolled glycosylation promoted by genuinely catalytic amounts of a catalyst (second step), are essentially completely fulfilled by the trichloroacetimidate method. This is clearly shown by the many examples and references given in this article. In terms of stability, reactivity, and applicability toward different acceptors, the 

Thanks are expressed to the Deutsche Forschungsgemeinschaft and to the Fonds der Che-mischen Industrie for financial support of our work reported in this chapter. 

Schmidt in W. Bartmann and K. B. Sharpless (Eds.), Stereochemistry of Organic and Bioorganic Transformations, Workshop Conferences Hoechst, Vol. 17, pp. 169-189. VCH Verlagsgesellschafl GmbH, Weinheim, 1987. 

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THE TRICHLOROACETIMIDATE METHOD AND OTHER ANOMERIC OXYGEN ACTIVATION METHODS FOR GLYCOSIDE SYNTHESIS... 

Other anomeric-oxygen exchange reactions have been recently investigated quite extensively. Closely related to the Koenigs-Knorr method is the introduction offluorine as the leaving group (Scheme 1, path B) (6,9-13). Because of the difference in halophilicity of this element as compared with bromine and chlorine, additional promoter systems besides silver salts were found useful as activators for glycosylation reactions (14-16). However,... 

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