A new synthetic route to 6-substituted-imidazo [4,5-c]pyridin-2-ons from 4-aminopyridine has been investigated. 4-Aminopyridine protected as alkyl carbamates were nitrated with dinitrogen pentoxide to the corresponding methyl, i-propyl and t-butyl 3-nitropyridin-4-yl carbamates (5 a-c) in 51-63 % yields. Attempts to substitute these in the 6-position by the ONSH and the VNS techniques succeeded with butylamine and the t-butyl carbamate 9.

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Oxidation of 5-hydroxyaminopyridine-2-sulfonic acid (1) to 5-nitropyridine-2-sulfonic acid (2) may be performed selectively by SPB in acetic acid, bleach in water or potassium permanganate in water, with the last as the preferred one. The structure of 2 was verified by X-ray crystallography. The crude products proved difficult to purify efficiently due to inorganic impurities, but substitution of the sulfonyl group in 2 with methanol yielded 2-methoxy-5-nitropyridine (6) in 44, 42 and 57 % overall yield from 1, respectively from the three methods. The reaction of 1 with SPC afforded 5,5'-azoxypyridine-2,2'-disulfonic acid (3) which, upon treatment with methanol gave 5,5'-azoxypyridine-2,2'-dimethoxypyridine (5) in 57 % yield from 1.

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