Imines tautomerism

Pyridin-4-one, 1 -hydroxy-2,6-dimethyl-hydrogen-deuterium exchange reactions, 2, 196 Pyridin-4-one, 1-methyl-hydrogen-deuterium exchange, 2, 287 pK 2, 150 Pyridin-2-one imine tautomerism, 2, 158 Pyridin-2-one imine, 1-methyl-quaternization, 4, 503 Pyridin-4-one imine tautomerism, 2, 158 Pyridinone methides, 2, 331 tautomerism, 2, 158 Pyridinones acylation, 2, 352 alkylation, 2, 349 aromaticity, 2, 148 association... 

The enamine-imine tautomerism of the indolenine system gives rise to rearrangement reactions of interest in indole alkaloid chemistry. Thus the synthesis of dihydroburnamicine (625) utilized the rearrangement of an acetoxyindolenine to an a-hydroxyalkyl indole, presumably through an intermediate enamine. Similarly 2,3-dialkyl indoles undergo oxidations to 2-acyl indoles (626-631). 

TL5981>. The proposed mechanism involves the oxidation of the amine to an imine, tautomerization to an enamine, and a sequence of nucleophilic attacks on the pyridazine rings followed by oxidation steps. The oxidant of choice is (bispyridine)silver permanganate <1982TL1847>, which is easily prepared, mild in action, and is soluble in organic media. If R1 = H in the product 77, electrophilic substitution (e.g., bromination, nitration, Mannich, and Vilsmeier-Haack-Arnold reactions) occurs at this position. 

Amine-imine tautomerism in 3-acyl-substituted aminopyrazines has been examined by H, C, and N spectral analysis as well as X-ray crystallography <2005JST67>. In the same way as the parent aminopyrazine, those aminopyrazines have been shown to exist in the amino form 11 (R = H, Me, Ph) (Scheme 2) in contrast to an expectation that the electron-withdrawing acyl groups adjacent to the amino substituent would stabilize the imino tautomers 12 and 13. Thus, all NMR spectra showed only existence of the amino tautomer 11, and additionally the... 

Garner et al. (90,320) used aziridines substituted with Oppolzer s sultam as azomethine ylide precursors. The azomethine ylide generated from 206 added to various electron-dehcient alkenes, such as dimethyl maleate, A-phenylmalei-mide, and methyl acrylate, giving the 1,3-dipolar cycloaddition product in good yields and up to 82% de (for A-phenylmaleimide). They also used familiar azomethine ylides formed by imine tautomerization (320). Aziridines such as 207 have also been used as precursors for the chiral azomethine ylides, but in reactions with vinylene carbonates, relatively low de values were obtained (Scheme 12.59) (92). 

C NMR data indicated the presence of a mobile formyl-enamine and enol-imine tautomeric mixture with the predominance of the former at 6-formyl-l,2,3,4,5,7,8,9-octahydro-ll//-pyrido[2,l-b]quinazolin-ll-ones (87JHC1045). 

Condensation of an amino acid-derived anilide and a /3-ketoamide afforded l,4-benzodiazepin-2-ones in which the initially formed imine tautomerizes to an exocyclic enamide (Scheme SO) <2001TL3227>. Only the (Z)-isomer of the enamide was isolated, assigned based on NOE data, and presumably reflecting stabilization by an intramolecular H-bond between the ring NH and exocyclic amide carbonyl. 

Knowledge of these rules was used to isolate individual tautomers of compound 429 [431] (Scheme 3.140). This heterocycle is crystallized from alcohols and chloroform in the imine tautomeric form B, while in trifluoroacetic acid solution the dimethylamino group undergoes a protonation leading to... 

In derivatives of dihydroazolopyrimidines containing the ortho-oxyaryl substituent (for instance, compounds 431) a sufficient factor stabilizing the imine tautomeric form is an intamolecular hydrogen bond [428, 429, 430] (Scheme 3.142). 

Meanwhile, Nikolay had started his new research on the preparation, reactions, and synthetic applications of p-chloro vinyl ketones and related compounds (p-aminovinyl ketones, p-kctoacetals). Efficient synthetic methods were developed and improved, including C-ketovinylation (introduction of the RCOCH = CH group), and a number of useful heterocyclic compounds (pyrazoles, triazoles, pyridines, and so on) were synthesized. The discovery of enamine-imine tautomerism in p-aminovinyl ketones was another remarkable achievement by Nikolay at that time. For these studies he received in 1953 the degree of Doctor of Science in chemistry. He continued as a lecturer and supervisor of postgraduates at the University, becoming docent (associate professor) in 1951 and full professor in 1955. 

The amine-imine tautomerism, liable to occur in aminopurines which may be illustrated in the particularly important case of adenine by the structures 6 and 7. 

Among the other possible isomeric aminopurines, some attention has been devoted to the amine—imine tautomerism in 2-aminopurine... 

The tertiary enamines, in contrast to the secondary derivatives, cannot exhibit enamine-imine tautomerism. As the free bases, they exist only in the vinylamino form. Their physico-chemical properties are in agreement with this structure, especially the spectral properties. The bands due to the stretching frequency of the carbon-carbon double bond in their infrared spectra1-25-27 (situated at 1630-1660 cm-1 according to the nature of the substituents) occur at somewhat lower frequencies, but their intensities are greatly increased in comparison to those of simple olefins because of conjugation with the free electron pair on the nitrogen atom. Indications of cis-trans isomerism... 

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