Enones unsaturated carbohydrates

Cycloaddition to a-P-unsaturated carbonyl systems represented by different carbohydrate enones yield annulated osides. These bicyclic molecules are used for synthesis of carbocyclic systems using the stereochemical information issued from sugar... 

These developments are here surveyed within the same guidelines as were used previously that is, discrete compounds will be dealt with which have one carbon-carbon multiple bond within the main sugar-chain. As before, enols, enediols, enones, dienes, and dienones will not be considered, nor will unsaturated cyclitols or heterocyclic compounds composed partially of acyclic carbohydrates. The first derivatives having carbon substituents attached by a double bond at a branch-point have now been prepared by application of the Wittig reaction to suitably protected glycosulose compounds these compounds are also arbitrarily excluded, as are ethers or acetals bearing unsaturated substituents. 

In previous investigations we could show that carbohydrate enones with the electrophilic terminus of the unsaturated carbonyl system at the anomeric carbon react with silyl enol ethers under catalysis of titanium tetrachloride, i. e. in a Mukaiyama-type reaction, to give the corresponding C-glycosides in high diastereoselectivity. The high stereocontrol observed could be explained in terms of a strongly adjusted cycloaddition-like transition state. This... 

Lithio-l-alkoxyallenes provide a,p-unsaturated acyl anion equivalents (Scheme 45). A series of chiral auxiliaries may be utilized for stereochemical control and the carbohydrate-based lithio species 215 and 216 provide a-hydroxyalkyl enones 217 in up to 88 %e.e. ... 

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