Reaction of substituted 1‐methyl(benzyl)pyridinium salts (1) with liquid ammonia/potassium permanganate leads to introduction of the imino group at the carbon adjacent to the nitrogen. The regiospecificity of the reaction strongly depends on substituent X: at C‐6 for X = H, CONH2, C6H5 and at C‐2 for X = CH3. 3‐Aminocarbonyl‐1‐t‐butylpyridinium iodide (5) on treatment with liquid ammonia/potassium permanganate exclusively gives the 4‐imino compound 8; 1H nmr spectroscopy shows that 5 in liquid ammonia gives a mixture of the σ‐adducts 4‐amino‐1,4‐dihydro‐ and 6‐amino‐1,6‐dihydro‐3‐pyridinecarbonamide (6 and 7). Surprisingly, an oxodemethylation reaction is observed on treatment of 3‐aminocarbonyl‐1,6‐dimethylpyridinium iodide (13) with liquid ammonia/potassium permanganate, 1,6‐dihydro‐1‐methyl‐6‐oxo‐3‐pyridinecarboxamide (14) being obtained. This compound can easily be converted by phosphorus oxychloride into the alkaloid nudiflorine (15).

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Syntheses of 2‐hydroxy‐4‐methoxypyridine, 4‐hydroxy‐2‐methoxypyridine, 4‐methoxy‐N‐methylpyridone‐2, and 2‐methoxy‐N‐methylpyridone‐4 are described. The ultraviolet absorption spectra of 50% aqueous ethanolic solutions of the above‐mentioned compounds and of 2,4‐dihydroxypyridine and 2,4‐di‐methoxypyridine are measured. Comparison of these spectra enables the determination of the predominant tautomeric structures of 2,4‐dihydroxypyridine and its derivatives. It appears that the chief structure of 2,4‐dihydroxypyridine in aqueous ethanol is that of 4‐hydroxypyridone‐2. Finally it is shown that the methyl derivative of 2,4‐dihydroxypyridine, obtained by Maquenne and Philippe ) when heating ricinine with hydrochloric acid solution or by conversion of 4‐methoxy‐N‐methylpyridone‐2 with the same reagent according to Späth and Tschelnitz ), is 4‐hydroxy‐N‐methylpyridone‐2.

When pyridine is heated with 100% sulphuric acid in the presence of mercuric sulphate as a catalyst at about 275°, pyridine‐3‐sulphonic acid is formed as the chief product, together with very small amounts of byproducts. The course of the reaction is more complicated at somewhat higher reaction temperatures. At 330° a mixture is obtained which contains, together with pyridine‐3‐sulphonic acid and the 4‐isomer, 4‐hydroxypyridine in considerable amount. The sulphonation of pyridine is a reversible process. When pyridine‐3‐sulphonic acid is heated with 100% sulphuric acid and mercuric sulphate at ∼ 330°, a mixture is formed containing chiefly pyridine, together with pyridine‐4‐sulphonic acid, 4‐hydroxypyridine and the starting substance.

Treatment of the 2‐R‐pyrimidines (1, R = methyl, ethyl, i‐propyl and t‐butyl) with potassium amide/liquid ammonia/potassium permanganate leads to amination at C‐4(6). The yields of the 4(6)‐amino compounds 3 in‐crease in the order 2‐methyl (10%), 2‐ethyl (30%), 2‐i‐propyl (45%) and 2‐t‐butyl (60%). Treatment of the 2‐R‐N‐methylpyrimidinium salts (4, R = hydrogen, methyl) with liquid ammonia/potassium permanganate leads to a regiospecific imination at C‐6, the corresponding 2‐R‐1,6‐dihydro‐6‐imino‐1‐methylpyrimidines 6 being obtained in 80‐85% yield. It is proved by 15N‐labelling that no ring opening is involved in these imination reactions. Treatment of the imino compounds with base leads to the corresponding 2.R‐6‐methylamino‐pyrimidines 8, involving, as proved by 15N‐labelling, an ANRORC‐mechanism. 2‐t‐Butyl‐1‐ethylpyrimidinium tetrafluoroborate (9b) when treated with liquid ammonia/potassium permanganate undergoes N‐deethylation, 2‐t‐butylpyrimidine being exclusively formed.