Effects of 5-acyl substituents on some properties of pyran-2,4-diones

The effects of 5-acyl substituents on the tautomerism of pyran-2,4-diones are revealed by comparison of the u.v.,i.r., 1H, and 13C n.m.r. spectral properties of 5-acetyl-6-methyl-,5-acetyl-6-phenyl-,5-benzoyl-6-methyl-, and 3,5-diacetyl-6-methyl-pyran-2,4-diones (3)–(6), with those of 6-methyl-(1) and 3-acetyl-6-methyl-pyran-2,4-done (2). The differences in the behaviour of the 5-acyl and 3-acyl derivatives towards primary amines are also discussed. Compound (6) reacts with aniline to form 5-acetyl-2,6-dimethyl-1-phenyl-4-oxopyridine-3-carboxylic acid (7).