Cyanopyridines quaternary salts, reactions with

Reaction of quaternary salt 226 with 4-melhylpiperidine gives rise to 4-(4-methylpiperidino)pyridine (277), which is a liquid, in contrast to the crystalline DMAP (228) and PPY (184) (83EUP74837). The reaction of 4-cyanopyridine (274) with acrylamide in the presence of HCI furnishes the crystalline quaternary salt 278, in quantitative yield, which is readily aminated with dimethylamine. Subsequent cleavage of the aminated quaternary salt by heating with strong alkali solution gives monomeric or... 

Formation of cyanides by replacement of hydrogen does not occur with pyridine, with pyridine l-oxide or 4-cyanopyridine l-oxide, but pyridinium quaternary salts are sufficiently electrophilic to react. Thus, 3,5-diethoxycarbonyl-1,2,4,6-tetramethylpyridinium methosulphate reacts with potassium cyanide giving 4(2 )-cyano-3,5-diethoxycarbonyl-l,2,4,6-tetramethyl-1,4(2 )-dihydropyridine. Various reactions of this kind have been studied in connection with the properties of diphosphopyridine nucleo-tide 4 . The cyano-dihydropyridines were isolated in several instances, and the addition process is reversible. The evidence seems to favour attack at C(4) but is not conclusive. Successful reactions have always been with quaternary salts containing electron-attracting substituents, usually at the... 

Of practical importance are the reactions of the quaternary salts of pyridine 1-oxides with aqueous potassium cyanide. The 1-methoxypyridinium methosulphates have usually been used, and with aqueous potassium cyanide, 2- and 4-cyanopyridine result [Table 5.25), the 2-position being somewhat favoured. A 3-substituent usually, but not always, causes 2-substitution to predominate over 6-substitution. The quaternary function is eliminated as an alcohol its presence probably determines the preference for 2- over 4-substitution, and its ready elimination makes the reaction a practicable source of cyanopyridines, in contrast to the case of other quaternary pyridinium salts (see above) with which reaction stops at the addition stage. These reactions are nucleophilic replacements not of hydride but of alkoxyl ... 

---