5-Iminocarboxylic acid esters

Dithiazines, urethanes, or iminocarboxylic acid esters result from the reaction of ethyl azidoformate with l,2-dithiole-3-thiones.232... 

Shin was unable to observe enamino-imino tautomerism in the case of dehydrovaline compounds (253, 373). E. Ohler and U. Schmidt (287, 350) were able to convert a-iminocarboxylic acid esters into a-enaminocarboxylic acid esters (42) by preparing the hydrochlorides of the former, which slowly rearranged into the hydrochlorides of the latter. This reaction is the simplest means of preparing a-enaminocarboxyhc acid esters, as the a-iminocarboxylic acid esters obtained by N-chlorina-tion/dehydrochlorination of amino acid esters can be rearranged directly, without intermediate purification. 

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. 

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. 

Sodium tert-butoxide a-Iminocarboxylic acid amides and a-hydrazinocarboxylic acid esters from 1,2-diazetidinones... 

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