Intramolecular hydrogen bonding and tautomerism of acylpyran-2,4-diones, -2,4,6-triones and acylpyridinediones and benzannelated derivatives. Deuterium isotope effects on 13C NMR chemical shifts

摘要: The structures of acylpyran-diones, -triones and acylpyridinediones have been studied primarily by deuterium isotope effects on 13C chemical shifts. 3,5-diacetyltetrahydropyran-2,4,6-trione forms a double tautomeric system involving one the carbonyl carbons anhydride moiety. This compound also exists as minor symmetrical isomer with two intramolecular hydrogen bonds to same acceptor. shows isotopic perturbation OH proton resonance upon deuteriation. A similar situation is found for 1,5-diphenylpentane-1,3,5-trione.The 3-acetyl-6-methyl-2H-pyran-2,4(3H)-dione be mainly in 4-hydroxy form. corresponding 5-acetyl derivative very weak bond 5-ethoxycarbonyl-6-methylpyridine-2,4(3H)-dione. pattern 3- 5-acetyl-6-methylpyridine-2,4(3H)-dione. difference two-bond effect related orders linking donors acceptors reflects strength bonds. 3-acetyl-4-hydroxy-2(1H)-quinolones are fashion.The formal hydroxypyridines shown 2-pyridone form.The imines most above compounds exist their keto-enamine forms. In case 3-(1-amino)ethylidenequinoline-2,4(1 H,3H)-diones 2-(1amino)ethylidene-6,7-dihydro-5H-benzo[ij]quinolizine-1,3(2H)-diones different either at C-4 or amide group C-2 observed. Deuterium shifts again turned out crucial structure elucidation.