NMR Spectroscopic Studies on the Tautomerism in Schiff Bases of Tenuazonic Acid Analogs

Abstract

Abstract A NMR spectroscopic study of 15N-enriched Schiff bases of such tenuazonic acid analogs as 3-acetyltetramic acid, 3-acetyltetronic acid, and 3-acetylthiotetronic acid showed the predominance of ketamine forms in their tautomeric equilibria in CDCl3. The ratios of “external tautomers” between two different ketamine forms, as calculated from the 15N–H signal intensities, were compared favorably with the ratios obtained from the ring methylene signals.