Quaternary pyridinium

Reactive halogen compounds, alkyl haUdes, and activated alkenes give quaternary pyridinium salts, such as (12). Oxidation with peracids gives pyridine Akoxides, such as pyridine AJ-oxide itself [694-59-7] (13), which are useful for further synthetic transformations (11). 

Fulvene-type enamines, which possess some nonbenzenoid aromatic character, have been synthesized by treating cyclopentadienylsodium with an amide-dimethyl sulfate eomplex (117aJ17b) or quaternary pyridinium salts (117c). One of the simplest ones produced is 6-(dimethylamino)fulvene (117a,117d). 

Partial hydrogenation of the quaternary pyridinium salts in the presence of triethylamine on palladium in methanol has been used for the synthesis of a large number of alkaloids. The tetrahydropyridine derivatives thus formed undergo various cyclization reactions in acidic media (89). 

Combination of the hydroxyl ion with the mesomeric cation involves the removal of a double bond. For the quaternary pyridinium compounds this causes the total loss of the aromaticity. For quaternary quinolinium and isoquinolinium compounds, the aromatic character of one of the two rings is lost, and for the quaternary acridinium compounds that of one out of three. Hence., the order of stabilities of these compounds (determined by Hantzsch ) is explained. - Comparison of quaternary 3,4-dihydroisoquinolinium compounds and their isoquinolinium analogs with respect to the equilibrium (5) (4) shows that a much higher hydroxyl ion concentration is necessary for the isoquinolinium ions to form the carbinolamine. This is because the transition from the quaternary 3,4-dihydroisoquinolinium ions into the undissociated carbinolamine involves significantly smaller loss of mesomeric energy than that for the quaternary isoquinolinium hydroxides. ... 

Tire and NMR parameters of some 1-alkyl-4-benzimidazolyl-2-idene- (type 72) and l-alkyl-4-(5-methylpyrazolyl-3-idene)-l,4-dihydro pyridines (type 73) were discussed in 89CC1086 and 91JOC4223. Comparison of the shifts for DMSO-dg and CDCI3 solutions with data reported for quaternary pyridinium compounds as well as anionic species in the azole series and data obtained for mesoionic betaines of the azinium azolate class left no doubt that these heterofulvalenes have a betaine character and, therefore, the NMR signals correspond to their dipolar resonance form. 

Of derivatives of compound 3, the zwitterions 245 react with DMAD if magnesium bromide is added to give aminopyridine derivatives (00H(53)265). Compounds such as 102 are opened by acid to give quaternary pyridinium salts (92LA885). There are various interconversions of 2-substituted triazolopyridin-3-ones into 1-substituted zwitterions. An example is the reaction of 246 (83BCSJ2969) the reverse conversion is also reported. 

With the two starting compounds, the picolylsulfone and the a-bromoketone we applied the well known Tschitschibabin synthesis (ref. 10). The first step of this synthesis is the formation of a quaternary pyridinium salt. 

N Bodor, E Shek, T Higuchi. Delivery of a quaternary pyridinium salt across the blood-brain barrier by its dihydropyridine derivative. Science 190 155-156, 1975. 

Zinc(II) phthalocyanines with quaternary pyridinium salt substituents are effective photobactericides for both Gram + ve (Enterococcus seriolicida) and Gram —ve (Escherichia coli Pseudomonas aeruginosa) bacteria.262... 

The effects of electron withdrawal by ring nitrogen are increased in pyridinium and related cations. Hence AAprotonation, AAalkylation or AAoxide formation results in greater substituent reactivity at the a- and y-positions. In quaternary pyridinium salts, e.g. (7),... 

The pyridine used in the submitters procedures apparently reacts with the sulfuryl chloride to form an intermediate quaternary pyridinium complex which undergoes aminolysis to yield the sulfamide. 1 However, in many instances the pyridine may be replaced by an equivalent, quantity of the primary... 

N. Bodor, R. G. Roller, and S. J. Selk, Elimination of a quaternary pyridinium salt delivered as its dihydropyridine derivative from brain of mice, J. Pharm. Sci. 67 685 (1978). 

Again, as expected, pyridine A-oxides are very susceptible to nucleophilic attack. Unlike the situation usually prevalent with the quaternary pyridinium salts, the elimination stage of the two-step nucleophilic substitution can occur with relative ease, the oxide grouping serving as a good sink for the leaving hydride ion electron-pair and being itself eliminated in the process. Considerably more work has been carried out on quinoline and isoquinoline A-oxides than on pyridine A-oxide derivatives. 

More than 130 different organic chemicals are currently employed as herbicides in the U.S. All of the main families of organic compounds are represented aromatic, aliphatic, and heterocyclic. Herbicidal activity is found in a variety of classes of compounds haloaliphatic, phenoxy, and benzoic acids carbamates dinitroanilines acetanilides amino triazines quaternary pyridinium salts uracils and ureas. A few selected key examples are reviewed below. 

Porphyrins bearing quaternary pyridinium substituents 93KGS723. 

The quaternary pyridinium chlorides are more easily hydrogenated than pyridine hydrochloride. Thus, A-phenyl- and IV-butylpyridinium chlorides were completely hy-... 

Reduction of quaternary pyridine salts with sodium amalgam afford the 1,2-dihydro whereas sodium hydrosulphite gives the 1,4-dihydro derivative, respectively362. From a preparative point of view, partial hydrogenation of quaternary pyridinium salts in alkaline media to give substituted 1-methyl-A2-piperideines is very important363,364. 

---