Glycosidation Noyori

Further improvements in the synthesis of pyruvated saccharide building blocks are achieved when the l,l,3,3-tetraisopropyl-l,3-disiloxane-l,3-diyl group (TIPS) is used for the Noyori-acetalation. 4,6-TIPS-protected glycosides such as 9 are conveniently prepared from the corresponding alkyl glycosides 8 in two steps and can be converted into the respective pyruvated glycosides 10 under essentially thermodynamic conditions [35b] (Scheme 2). 

Noyori and Kurimoto [330] have found an interesting anodic ether exchange reaction of aryl glycosides. They described that this is a rate example of SoNl-type transformation reaction, but the reaction may be EGA (electrogenerated acid)-catalyzed. The reaction is also stereoselective but not always stereospecific. 

Noyori and Kurimoto [240] described that hydroxyl-protected and -unprotected glycosyl ary-loxides reacted with alcohols under mild electrolytic conditions to give the corresponding glycosides. They hypothesized that the glycosylation reaction proceeded via oxocarbenium ion intermediates generated from the radical cation of the easily oxidizable aryloxy substrate (O Scheme 84). 

A new general approach to the synthesis of C-glycosidic compounds and C-nucleosides was elaborated by Noyori. In his approach the starting material, unsaturated bicyclic ketone 236, was prepared in a cyclocoupling reaction between 1,1,3,3-tetrabromoacetone and furan, followed by a zinc-copper couple... 

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