Alkylpyridines quaternary salts

Nitrosation of 2- and 4-alkylpyridines, their quaternary salts and N-oxides, can be effected with an alkyl nitrite and sodamide in liquid ammonia the product is an oxime (Scheme 54) (69AP494, 65YZ451). 

Pyridinium quaternary salts 3.266 are, on the other hand, easily reduced by AIH3 or LAH in ether media, Red-Al in CgH, or alkaline borohydrides in alcoholic media, leading to the 1,2,3,4-tetrahydro-N-alkylpyridines. If diastereoisomers can be generated, the stereoselectivity is usually poor [DG2], When the pyridinium salt... 

In the quaternary salts of alkylpyridines, the side-chain hydrogens are considerably more acidic and condensations can be brought about under quite mild conditions, the reactive species being an enamine " side-chain deprotonation of 7V-oxides can also be achieved, though it can be complicated by ring deprotonation at C-2. 

An alternate route to styrylpyridinium polymers [30] uses sulfonate esters of polyvinyl alcohol which are quaternized with alkylpyridines. The quaternary salts are then caused to react with various aldehydes. 

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