Pyridinium salts, l-

An extension of this synthetic route to tetracyclic systems of type 36 was described by Thesing and his co-workers, who reduced the /3-(3-indolyl)ethyl-l-pyridinium salt 55 (R = H) catalytically and... 

Considerable rate enhancements are observed upon quaternization of the pyrimidine ring, due to its electron-deficiency. Heating of the l-ethyl-2-(pent-4-yn-l-yl)-5-phenylpyrimidinium tetrafluoroborate (X = CH2) at 180°C for 15 min ( ) gave in a more or less quantitative yield 1-ethyl-6,7-dihydro-3-phenyl-5//-l-pyridinium salt (X = CH2) (90T595) (Scheme 36). A similar reaction was also observed with the 2-(butynylthio)pyrimidinium salt (X = S). 

This method is not general and only a limited number of 5-alkyl-l,2,3,4-thiatriazoles were prepared by this reaction. Ikeda and co-workers have described a convenient method for the synthesis of both 5-alkyl- and 5-aryl-l,2,3,4-thiatriazoles 9 by reaction of l-methyl-2-thioacylpyridinium salts 143 with sodium azide (Scheme 33). Compound 143 can be prepared from pyridium salt 142 by reaction with dithiocarboxylic acid derivatives. The synthesis can conveniently be carried out as a one-pot reaction from 2-chloro-l-pyridinium salt 142 and carbodithioate leading to final compounds 9 in high yields. The 5-alkyl-l,2,3,4-thiatriazoles 9 were isolated as oils <1990S415, 1990ZC67>. 

Alkylideneamino)sulfonium salts S-Alkylthiolactims 1-Alkylthio-l-pyridinium salts S-Aminosulfonium ylids... 

N-Thiogly cosyl-N -heterocy dies from 1-alkylthio-l-pyridinium salts... 

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). 

The 3-chloroacrylaldehyde (218) (Type 1, Scheme 6) reacted readily with 2-amino-l,3,4-selenadiazole (219). The final product was the [l,3,4]selenadiazolo[3,2-a]pyridinium salt (220) (76ZC337X... 

Pyridinium salts, l-aryl-4-methoxy-2,6-dimethyl-synthesis, 3, 762 Pyridinium salts, N-aryloxy-rearrangements, 2, 354 Pyridinium salts, 1-benzyl-covalent amination, 2, 239 Pyridinium salts, N-benzyl-reactions... 

Pyridinium salts, l-ethoxy-4-methyl-thioalkylation, 2, 230 Pyridinium salts, N-ethyl- H NMR, 3, 893 Pyridinium salts, 2-halo-nucleophilic reactions, 2, 360 N-oxides... 

Pyridinium salts, 4-methoxy-l-methyl-3-nitro-reduction... 

A special type of ammonio group is represented by 4-( 1 -pyridinium)-pyridine and other azinium analogs. Such products often result from self-quaternization of highly reactive derivatives. A -(4-Pyridyl)-and A -(3-nitro-4-pyridyl)-pyridinium chloride hydrochlorides (121) react with aniline, chloride ion, and water to give 4-substituted pyridines plus pyridine. l-(2-Quinolyl)- and l-(4-quinolyl)-pyridinium salts undergo 2- and 4-substitution, respectively, with amines, anilines, hydroxylamine, phenols, alkoxides, mercaptans, and chloride... 

Over the last decade V-(l-haloalkyl)pyridinium salts and analagous compounds have been developed as important synthetic reagents. In a joint contribution from the Universities of Friedrich Schiller, Germany, and Mons, Belgium, Professors E. Anders and J. J. Vanden Eynde and Dr. K. Wermann give an authoritative account of these interesting and important compounds. 

The nitration of l,2,5-selenadiazolo[3,4-/] quinoline 77 with benzoyl nitrate affords the 8-nitro derivative 78, whereas methylation with methyl iodide or methyl sulfate afforded the corresponding 6-pyridinium methiodide 79 or methosulfate 80, respectively (Scheme 29). The pyridinium salt 80 was submitted to oxidation with potassium hexacyanoferrate and provided 7-oxo-6,7-dihydro derivative 81 or, by reaction of pyridinium salt 79 with phenylmagnesium bromide, the 7-phenyl-6,7-dihydro derivative 82. Nucleophilic substitution of the methiodide 79 with potassium cyanide resulted in the formation of 9-cyano-6,9-dihydroderivative 83, which can be oxidized by iodine to 9-cyano-l,2,5-selenadiazolo [3,4-/]quinoline methiodide 84. All the reactions proceeded in moderate yields (81IJC648). 

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