Alkyl glycosides, synthesis preparative usefulness

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). 

The synthesis of a variety of stable carbohydrate mimetics using a RCM approach is discussed. An esterification-ring-closing metathesis (RCM) approach has been utilized for the preparation of a variety of alkyl and aryl C-glycosides. The synthesis of a number of C-saccharides will also be addressed. Yield optimization studies and the synthesis of the substrates will also be discussed. 

Applications of the same enolate alkylation procedure to furnish gem-dialkylated compounds have been used in the synthesis of onnamide A [118]. This type of gem-2-C-dimethyl group is also found in pederin and mycalamides A and B. As shown from the retrosynthetic analysis of some members of this class of compounds (Scheme 11.38), C-glycosidic structure 158 could be obtained from the a-glycoside 159. The latter could be prepared from the ketone 160 via gem-dialkylation of the corresponding enolate, as described for the synthesis of 8. 

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