Iminocarboxylic Acid Derivatives

Most syntheses of iminocarboxylic acid derivatives start from a-keto acids or a-amino acids. Thus Appel and Hauss 12) described the formation of a-iminopropionic acid ester by treatment of pyruvic acid ester with triphenylphosphine imine. This product was however not isolated, but hydrogenated directly to the corresponding alanine ester. 

Shin et al. 253, 373) applied the same reaction to an ester of dimethylpyruvic acid and were able to isolate and characterize the a-iminovaleric acid ester containing no detectable amount of tautomeric enamine. Other reactions of N-triphenylphosphine imine with various a-keto esters have been found to yield tautomeric mixtures 371). 

N-Alkyliminoacetic esters have been obtained by Massen et al. 254) by addition of phosphonate carbanions to tert. nitrosoalkanes. 

Fiaud and Kagan 125) condensed glyoxylic acid menthyl ester with benzylamine or a-substituted benzylamines to form the corresponding N-benzyliminoacetic acid menthyl esters. 

N-Chlorination/dehydrochlorination of amino acid esters 310) is the simplest route to a-iminocarboxylic acid esters. With the exception of the leucine derivative, which was obtained as a tautomeric mixture, no enamine could be detected in the products by NMR spectroscopy. Phenylalanine ester yielded the enaminoacid ester exclusively. 

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B. Addition Reactions to a-Acylimino- and a-Iminocarboxylic Acid Derivatives 297... 

Dehydroamino Acids, a-Hydroxy-a-amino Acids and a-Mercapto-a-amino Acids 281 E. CK-Iminocarboxylic Acid Derivatives... 

By addition of pyruvoyl chloride to a-iminocarboxylic acid derivatives 295a, 295b, 311). 

Other iminocarboxylic carboxylic acid derivatives have been prepared by reacting an hydroxyimino derivative with 2-coumaranone followed by the Pinner reaction of the Step 1 product (2,3) as illustrated in Eq. 4 ... 

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