3- Aminopyridines 3-pyridyl pyridinium

Fluoropyridine. This isomer can be prepared in 54—81% yield by dia2oti2ation of 4-aminopyridine in anhydrous hydrogen fluoride (370,371,400). Eree 4-fluoropyridine readily undergoes self-quaterni2ation to give pyridyl pyridinium salts (401) stabili2ation can be effected as the hydrochloride salt (371,400). Numerous 4-fluoropyridinium salts, eg, 4-fluoro-l-methylpyridinium iodide, have been converted to novel penicillins (387,402). 

Improved procedures for the Chichibabin amination of pyridine derivatives have been reported (83JAP(K)58-208266, 83USP4386209, 83USP4405790). A general method has been developed for the conversion of 2-aminopyri-dines into 2-pyridones via 2-cthoxycarbonyl-l-(2-pyridyl)pyridinium ions 15. The pyridinium ions 15 are easily made from the 2-aminopyridines 14 and the corresponding pyrylium salt 13. On treatment with aqueous sodium hydroxide, pyridinium ions 15 are converted into the l-(substituted-2-pyridyl-carbonyl)-2-pyridones 16, which are readily hydrolyzed to the 2-pyridones 17 and the picolinic acid 18 (83JCS(P1)2623). 

This reaction (a) has considerable preparative interest in the case of l-(4-pyridyl)pyridinium salts since it permits introduction of an amino group at position 4 of pyridine. For example, 4-aminopyridine is formed when l-(4-pyridyl)pyridinium chloride hydrochloride is heated with aqueous ammonia for 8 hours at 150°1136 or when ammonia is led into a solution of this salt in phenol for 3 hours at 180-190° (80% yield).1137 Analogously, passing dimethyl-amine into a phenol melt of the salt gives 4-(dimethylamino)pyridine.1138 Under these conditions the quaternary pyridine ring is easily cleaved by aromatic amines, so that 4-(arylamino)pyridines are better synthesized from the pyridylpyridinium salts by means of the hydrochloride of aromatic amines.1139... 

UV-Vis absorbing electrolytes Creatinine, Imidazole, ephedrine, pyridine, copper sulfate, 4-aminopyridine, 4-methylbenzylamine, benzimidazole, p-toluidine, /V,/V -dimethylamine, malachite green, o-aniline, 1-(4-pyridyl)pyridinium All analytes Most universal and can be applied to many non-UV absorbing analytes If a suitable buffer system Is selected... 

Heating l-(4-hydroxy-2-pyridyl)pyridinium chloride in aniline and acetic anhydride gives a product that, on hydrogenation over palladium-charcoal, proved to be 2-aminopyridine. ... 

Aminopyridines from ethylenepyridinium salts via (3-pyridyl)pyridinium salts... 

A mixture of l-methylanilino-4-pyridinio-5- (p-bromophenyl) -l,3-pentadien-5-one bromide, NH4-acetate, and glacial acetic acid heated 30 min. in an oil bath at 150°, cooled, and treated with 70%-HClO4 -> N-[2-(p-bromophenyl)-3-pyridyl]-pyridinium perchlorate (Y 83%) treated with hot piperidine for 0.5 hr. 2-(p-bromophenyl) -3-aminopyridine (Y 76%). F. e. s. K. Dickor and F. Krohnke, B. 95,2479 (1960). 

Reaction of pyridinium-A -(2-pyridyl)amidine (402) and alkyl haloace-tates in the presence of K2CO3 afforded a mixture of 4-oxo-4/f-pyrido[l, 2-u]pyrimidine-2-carboxylates 407 and 2-aminopyridine derivatives 406 through intermediers 403- 05, as depicted in Scheme 15 (00TL5837). Compound 406 could be cyclized on the action of heat or silica gel into 407. The best yield was achieved in the case of ethyl bromoacetate. 

The regioselective halogenation of pyridinium-A -(2 -pyridyl)aniinide 7 with N-halosuccinimides, combined with a reduction of the N-N bond, provides a convenient preparation of 5-halo- and 3,5-dihalo-2-aminopyridines 8 <95T(51)8649>. 

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