From N-Hydroxyamino Acid Derivatives

Acylenamino Carboxylic Acid Derivatives From N-Hydroxyamino Acid 

Shin et al (377) developed an additional route to N-acylenamino-carboxylic acid esters, starting from N-hydroxyamino acid esters N-acyl-hydroxyamino acid esters and N,0-diacyl-hydroxyamino acid esters, obtained by mono- or diacylation respectively, eliminate water or carboxylic acid respectively on treatment with triethylamine. The acyl-imino compounds probably formed initially isomerize spontaneously to the acylenamino compounds. Kishi et al (274) have described an analogous sequence for the preparation of N-acetyldehydroalanine ester. 

Acylenamino Acid Esters from Carbonyl Compounds and Isocyanoacetic 

ScHOLLKOPF et al (360) reacted a-metallated isocyanoacetic ester with aldehydes and ketones in aprotic solvents to form formyl-enamino acid esters (24) via intermediate oxazoline carboxylic acid esters. 

Applied to unsymmetrical ketones, the synthesis yields ZjE mixtures. The NMR spectra of the components allow the appropriate configurations to be assigned. The reaction has also been exploited by other authors (75), for example to introduce branched chains into ketoses. 

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