Ulosonic acid strategies towards

Much effort towards stereoselective synthesis of 3-deoxy-2-ulosonic acids resulted in the development of several strategies based on the diverse building units. Among them aldol reaction between D-arabinose derivative 50 and methyl dichloroacetate (51) deserves some attention [78] (Scheme 14). The condensation product isolated as oxirane derivative 52 reacted smoothly with Mgk to give the intermediate 53, easily convertible into 3-deoxy-D-ara6mo-2-heptulosonic acid methyl ester 56 in high yield. 

Among various strategies towards ulosonic acids various acylation reactions are often used. They involve alditol derivatives as convenient substrates, and diverse acyl anion equivalents. Here belongs the synthesis of KDO, developed by Shiba et al. [84], By reaction of the triflate 67 with the lithiated 68, eight carbon atoms compound 69 was obtained (Scheme 17). Removal of O-acetyl residue with subsequent NBS promoted oxidative hydrolysis of the dithioacetal moiety resulted in the formation of KDO derivative 70. 

Enders also applied a proline-catalyzed strategy to develop a direct biomimetically inspired route towards precursors of ulosonic and sialic acids (60) as demonstrated in... 

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