NMR Spectroscopic Studies of the Tautomerism in Tetramic Acid Analogs and Their Anilides. III. Polar Solvent Effects on the Tautomeric Populations

Abstract

NMR spectroscopic studies of 3-acetyltetramic acid (3-acetyl2,4-azolidinedione), 3-acetyltetronic acid (3-acetyl-2,4-oxolanedione), 3-acetylthiotetronic acid (3-acetyl-2,4-thiolanedione) and their anilides (3-(2-phenyliminoethyl) derivatives) showed variations in the tautomeric equilibria with certain polar solvents. For example, the strong solvation effect of DMSO-d6 causes a predominance of the lactim forms of 3-acetyltetramic acid over the lactam forms and up-field shifts of the enolic protons.