Branched-chain sugars Wittig reaction

Rosenthal, A, Sprinzl, M, Branched-chain sugar nucleosides. IV. 9-(3-deoxy-3-C- hydroxymethyl -P(and a)-D-allofuranosyl and ribofuranosyljadenine. Can. J. Chem., Al, 4477-4481, 1969. Rosenthal, A, Catsoulacos, P, Synthesis of branched-chain sugars by the Wittig reaction. Can. J. Chem., 46, 2868-2872, 1968. 

Rosenthal, A., and L. B. Nguyen New Route to Branch-Chain Sugars by Application of Modified Wittig Reaction to Ketoses. Tetrahedron Letters 1967, 2393. 

The main interest in unsaturated sugars prepared by the Wittig reaction (and described in this Section) has concerned their synthetic utilization. The pathways of the latter depend on the structure of the unsaturated precursor. In the case of C-glycosylated alkenes, addition to the double bond (mainly hydration and hydrogenation) leads to a branched-chain or long-chain sugar, although correct choice of the reactant to be added may provide a variety of derivatives. 

A number of more complex structures, useful in total syntheses, are accessible from olefins formed by Wittig olefinations of keto-sugars. A fmitful reaction is the dihydroxylation of double bonds. Obviously, methylene derivatives will give the hydroxymethyl branched-chain derivatives. 

Rosenthal, A., and Baker, D.A., New route to branched-chain amino sugars by application of modified Wittig reaction to ketoses. Tetrahedron Lett., 10, 397, 1969. 

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. 

A Wittig reaction was used to prepare the methoxymethylene branched-chain amino-sugar (38), which was then modified conventionally to the diacid derivative (39) and hence converted to thienamycin (described in Chapter 23).Another synthesis of thienamycin from the same 3-azido-2,3,6-trideoxy-D-arabino-hexoside precursor used for preparing (38) adopted a double inversion technique to make the 4-C-cyano sugar (40), displacing triflate esters first by acetate and then by cyanide (18Ji overall yield). 

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