Decarboxylation dihydroxyfumaric acid

Some of the earliest kinetic studies on metal ion-promoted reactions were carried out on metal ion-promoted decarboxylations of j8-oxo acids. The literature on this topic up to about 1974 has been reviewed. Much of the work has centred on oxaloacetic acid (HO2CCOCH2CO2H = H20xac) and its derivatives, a,a-dimethyl oxaloacetic acid and fluorooxaloacetic acid. Studies have also been made with acetonedicarboxylic acid (3-oxoglutaric acid), " dihydroxyfumaric acid, dihydroxytartaric acid, acetosuccinic acid, oxalosuccinic acid and 2-oxalopropionic acid (Figure 6). The decarboxylation of )3-oxo acids is of considerable biological importance, and in a number of cases metalloenzymes are involved. Similarities in the enzymatic and chemical processes stimulated early interest in these reactions as models for the enzymatic systems. 

An interesting application of this method is a convenient synthesis of the parent oxazole.124 186 It is prepared by oxidizing tartaric acid with hydrogen peroxide to dihydroxyfumaric acid (55), the methyl or ethyl ester of which is condensed with formamide in the presence of hydrogen chloride to give 4,5-dialkoxycarbonyloxazole (56, R = Me or Et), which is saponified with aqueous barium hydroxide or alcoholic sodium hydroxide. The anhydrous salt is then decarboxylated to oxazole, without isolation of the comparatively unstable 4,5-oxazoledicarboxylic acid, in 55-70% yield. 

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