2-Methylpyridinium salts

A number of 2-aryl derivatives were obtained by oxidation of the 2-methylpyridinium salts 247 in refluxing pyridine.202... 

Interest in the use of pyrylium salts in synthesis continues. 2-Methylpyridinium salts are converted into the 2-arylpyridinium compound on reaction with 2,4,6-triarylpyrylium salts in the presence of base. The methylpyridinium salt is deprotonated to the anhydrobase which behaves as an enamine, attacking the pyrylium salt at C-2, promoting a ring opening - ring closure sequence which culminates in the effective arylation of the pyridinium salt. 

Westphal condensation of acenaphthenequinone with 1-ethoxycarbon-ylmethyl-2-methylpyridinium salt and 2-ethoxycarbonylmethyl-l-methyl-isoquinolinium salt in the presence of sodium acetate gave 251 (73%) and 252 (44%), respectively (86JHC1151). On heating 251 with HBr, parent compound 253 was obtained (48%) (85JHC681 86JHC1151 89H2369). 

A modified synthetic route to 3-isopropyl-l//-2,l,3-benzothiadiazin-4(3//)-one 2,2-dioxide (215) (Bentazon) (Section 6.16.12) involving sulfonylation of the 2-aminobenzamide (213 R = R = H) at the amine function with 2-methylpyridine-sulfur trioxide complex, followed by cyclization of the resulting 2-methylpyridinium sulfonate salt (214) with hot phosphorus oxychloride has been patented (Scheme 26) <89CZP257059, 91CZP270529). The reaction kinetics, particularly the cyclization of the 2-methylpyridinium salt (214), have been subjected to a detailed investigation <89Mi 6i6-02>. 

Cyclization of 2-aminobenzamide derivatives constitute the main synthetic approach to the 2,1,3-benzothiadiazine nucleus. 2,l,3-Benzothiadiazin-4(3//)-one 2,2-dioxides are available by the action of sulfamoyl chloride on methyl anthranilate, by treatment of 2-methylpyridinium salts of 2-sulfamoylbenzamides with phosphorus oxychloride (Section 6.16.9.1.2), by base-catalysed cyclization of A -(2-aminocarbonyl)sulfamides (Section 6.16.9.1.2), and by cyclization of 2-amino-benzamides with thionyl chloride (Section 6.16.2.3.1). 

A base treatment of 2-methylpyridinium salt of Baylis-Hillman bromide generated via an A-allylenamine intermediate results in a 3-aza-Cope rearrangement. ... 

As part of a program to synthesize ipecac alkaloids, dipyridinium diiodides (XII414), which are formed from l,5-disubstituted-2-methylpyridinium salts and iodine in pyridine, were converted to 2-pyridones (XII-41S) with aqueous... 

YAG 93] Yagci Y., Lukac 1., Schnabel W., Photosensitized cationic polymerization using N-ethoxy-2-methylpyridinium salts . Polymer, vol. 34, pp. 1130-1133, 1993. 

Degradation of a,) ethyleneketones to ketones via Beckmann rearrangement s. 11,317 2-Pyridones from 2-methylpyridinium salts... 

Interestingly, when iV-ethoxy-2-methylpyridinium salt is added to the mixture consisting of a monomer (methyl methacrylate) and thioxanthone, a significant enhancement of the polymerization rate is detected [147]. This effect has been attributed to a reaction of ketyl radicals stemming from thioxanthone with the pyridinium salt, which leads to the generation of initiating ethoxy radicals. 

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