Acetamide Tautomerism

The carbon-carbon double bond of an unsaturated AA reacts with 1,3-dipoles to give derivatives of pyrazole or isoxazole. When methanol is used as a solvent, the 1-pyrazolines primarily formed are tautomerized into 2-pyrazolines, which may eliminate benzamide or acetamide to give aromatic pyrazoles (Scheme 19) (88JHC851). Aromatization may also be affected with BF3 Et20. The cycloadditions are stereospecific (85JOC3167). In a... 

DFT calculations on the Mg(L—H)(L) complex reveal how water and acetonitrile can be lost (Scheme 9). Thus intramolecular proton transfer tautomerizes the neutral acetamide ligand in 48 into the hydroxyrmine form in 49, which can then dissociate via another intramolecular proton transfer to yield the four-coordinate adduct 50, which now contains both water and acetonitrile ligands. It is this complex that is the direct precursor to water and acetonitrile loss. Note that the reaction shown in Scheme 9 is a retro-Ritter reaction and involves fragmentation of the neutral rather than the anionic acetamide ligand, which is a bidentate spectator ligand. 

A tautomeric equilibrium between enamine and methylene imine forms has been demonstrated to exist in 2-(3,4-dihydro-3-oxo-2(l//)-quinoxalinylidene)-Al-phenylacetamides and 3,4-dihydro-3-oxo-/V-phenyl-2-quinoxaline acetamides when these are in DMSO solution either in the absence or presence of TFA [95JHC671]. The reduction potentials of some pyrazines and their benzo-fused analogs have been summarized as part of an EPR study of the electron transfer interaction between nitrogen heterocycles and n-B N+BHf [95JOM123]. 

Instead of the nucleophilic N-atoms, the attempted attack of appropriate carbanions (from acetamides substituted with an electron-withdrawing group) on the C-6 position of dimethyluracil leads to the cleavage of the uracil ring. This reaction splits off dimethylurea and leads finally to the formation of tautomeric pyridine-2,6-diones, such as 2,6-dihydroxynico-tinamide. Similarly, the reaction of 1,3-dimethyl-4-thiouracil with malo-namide proceeds smoothly to give 2-hydroxy-6-mercaptonicotinamide (791A4423 81JOC846) (Scheme 136). 

This reaction indicates that the nitrogen in acetamide is linked to the carbon which is in accord with both of the tautomeric formulas just given. This methyl cyanide, it will be recalled, is readily hydrolyzed to the acid requiring, however, two molecules of water. Acetamide therefore, is an intermediate step in the hydrolysis of an alkyl cyanide, acid nitrile, to an acid. Writing the general reaction in steps we have,... 

The monomer VAm is not available due to the well known tautomerization equilibrium with acetaldehyde imine. Therefore, polymer-analogous reactions must be employed to synthesize PVAm from suitable precursor polymers, e.g. poly(acrylamide) [53, 54], poly(vinyl acetamide) [55], poly(vinyl carbamate) [56], or poly(vinyl imides) [57]. Some of these polymer-analogous reactions require rather rigorous reaction conditions and side-products and degraded polymer chains disturb the properties of the final product. 

Azocompounds Acetamides Aromatic/Heterocyclic amines Nitro compounds Nitrenium ions, tautomeric carbonium ions... 

The authors proposed a mechanism in which acetamide adds to the a-acyloxy-ketone 422 to produce an iV-acylimine 424 that tautomerizes to an iV-acylenamine 425. Cyclization of 425 followed by deacetylation and dehydration furnishes 423 (Scheme 1.116). Other catalysts, including H2SO4, P2O5, SOCI2, and polypho-sphoric acid, were ineffective. 

N-[Cyclohexyl-(2-nitrophenyldithio)methylene]acetamide heated in CCI4 tautomeric aminovinyldisulfide. Y 80-90%. F. e., also direct prepn. from thioamides and sulfenylchlorides, s. W. Walter and H.W. Meyer, A. 1973, 462 1974, 776. 

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