2- pyridines, tautomerism

Buil ML, Esteruelas MA, Garcs K, Olivn M, Oate E (2007) Understanding the formation of N-H tautomer from a-substituted pyridines tautomerization of 2-ethylpyridine promoted by osmium. J Am Chem Soc 129 10998-10999... 

Oxygen Substituents. The presence of oxygen or sulfur attached to the ring can affect the chemistry of those compounds through tautomerism. This phenomenon ia the pyridine series has been well studied and reviewed (38). An example of 2-pyridone—2-pyridinol tautomerism was shown ia equation 2, compound (16). 

Table 11 summarizes the main results on the tautomerism of mono-hydroxy-, -mercapto-, -amino- and -methyl-azines and their benzo derivatives, in water. At first sight the equilibrium between 2-hydroxypyridine (71) and pyridin-2-one (72) is one between a benzenoid and a non-benzenoid molecule respectively (71a 72a). However, the pyridinone evidently... 

For the NH azoles (Table 3), the two tautomeric forms are usually rapidly equilibrating on the NMR timescale (except for triazole in HMPT). The iV-methyl azoles (Table 4) are fixed chemical shifts are shifted downfield by adjacent nitrogen atoms, but more by a pyridine-like nitrogen than by a pyrrole-like iV-methyl group. 

Pyrazolo[ 1,5-n Jpyridine, 2-hydroxy-tautomerism, 5, 309 Pyrazolo[3,4-6]pyridine, 3-bromo-synthesis, 5, 315... 

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