5 -carboxamide tautomerism

Benzo[c]furan, 1,3,4,7-tetraphenyl-steric hindrance, 4, 542 synthesis, 4, 683 Benzo[b]furan-3-acetic acid synthesis, 3, 686 Benzo[b]furan-3-amine, 2-acyl-tautomerism, 4, 648 Benzo[b]furan-2-carboxamides synthesis, 3, 685... 

C NMR, 6, 398 molecular dimensions, 6, 397 tautomerism, 6, 404 Furoxan-3-carbohydra2ide intramolecular hydrogen bonding, 6, 396 Furoxan-3-carboxamide intramolecular hydrogen bonding, 6, 396 Furoxancarboxylic acids reactions, 6, 413 with nucleophiles, 6, 406 Furoxan-3,4-dicarbaldoxime synthesis, 6, 409 Furoxanoaaines fused... 

Pyridazine-3-carboxamide, 1,6-dihydro-6-oxo-analysis, 3, 2 tautomerism, 3, 4 Pyridazinecarboxamides synthesis, 3, 33... 

Proton acidity in oxazole follows the order C-2 > C-5 > C-4. The use of 2-lithiooxazoles in synthesis is problematic, however, because they are in tautomeric equilibrium with their open chain form. When 2-lithiooxazole was reacted with DMF at — 75°C and the mixture was warmed to RT, oxazole-2-carbaldehyde (53) was formed quantitatively. Reaction of this product with a second equivalent of lithiooxazole did not give the expected product, but rather an unsymmetrical bis(oxa-zolyl)methanol (54) <9iJOC449> (Scheme 12). Reaction at the 4 position of lithiooxazole was found to be general for aldehydes. Less reactive electrophiles, such as, DMF, benzophenone, and ethyl formate, gave 2-substituted products, and iodobutane, benzyl bromide and ethyl carbonate did not react at all after an extended age at RT. Acylation of 2-lithio-5-phenyloxazole may be accomplished using A-methyl-7V-(2-pyridinyl)-carboxamides <84S1048>. 

Three proposals for the mechanism of metal-depending nitrile hydratases have been suggested, the most plausible assumes direct corrdination of the nitrile to the metal, which (by acting as Lewis-acid) increases the electrophilicity of the carbon atom to allow attack of a water-molecule. The hydroxy-imino-species thus formed tautomerizes to form the carboxamide [638-640]. 

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