2-Chloro-5-hydroxypyrazine chlorination

Pyrazines with hydroxyl groups are generally in the oxo form however, substituents like chlorine may profoundly influence the position of the tautomeric equilibria. Ultraviolet measurements indicate that in ethanol solution 2-chloro-6-hydroxypyrazine (125a) exists predominantly in the hydroxy rather than in the oxo form (125b) 272 trifluorohydroxypyrazine also does not tautomerize appreciably to a pyrazinone.279... 

Ring substituents of pyrazine A-oxides show increased reactivity, and substituents in the a-position to the A7-oxide function are more reactive than those in the /3-position. Thus, 2-chloropyrazine 1-oxide is converted into the 2-hydroxy-1-oxide on mild alkali treatment,398 but attempts to carry out a similar reaction with the 2-chIoro-4-oxide were not successful.412 Ammonolysis of the 2-chloro-4-oxide has been achieved, and nitrous acid treatment of the resulting 2-amino-4-oxide gives 2-hydroxypyrazine 4-oxide (Scheme 46). The chlorine atom of both isomeric 2-chloropyrazine A-oxides is readily displaced with sulfanilamide to give the corresponding sulfanilamidopyrazine A-oxides.413,414... 

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