2-amino-2- - pyridinium salt

Most of the synthetic approaches toward this ring system utilize N-amino pyridinium salts functionalized at the a-position with a carbonyl group. Thus, the amination of 2-(l,3-dioxolan-2-yl)pyridine with tosyl-hydroxylamine gave 78, whose reaction with urea in the presence of boron trifluoride-acetic acid gave 79, which gave the thermally unstable... 

A 2-aminophenylacetate spontaneously cyclizes in acetic acid or with PPA [2416] to give an oxindoie. An unexpected cyclization observed when the amino-pyridinium salt (48.1) is heated with benzylamine is a Dimroth rearrangement. 

Pyrazolo[l,5-a]pyridines can be prepared by cycloaddition of pyridinium A -imides (produced by iV-deprotonation of iV-amino-pyridinium salts with base ) with alkynes or A -amination of 2-alkynyl-pyridines. The cycloaddition of 3-benzyloxypyridinium AT-imide involves preferentially the more hindered C-2. ... 

Amino-5-nitrosopyrimidines also condense with benzoylacetonitrile, phenacyl-pyridinium bromide and acetonylpyridinium chloride in the presence of sodium cyanide to produce. 7-amino-6-pteridinyl ketones (63JOC1197). Pteridine syntheses from pyridinium salts are not limited to the preparation of pteridyl ketones since pyridinium acetamide... 

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... 

The configuration of the amine was retained, except in the case of amino acid derivatives, which racemized at the stage of the pyridinium salt product. Control experiments showed that, while the starting amino acid was configurationally stable under the reaction conditions, the pyridinium salt readily underwent deuterium exchange at the rz-position in D2O. In another early example, optically active amino alcohol 73 and amino acetate 74 provided chiral 1,4-dihydronicotinamide precursors 75 and 76, respectively, upon reaction with Zincke salt 8 (Scheme 8.4.24). The 1,4-dihydro forms of 75 and 76 were used in studies on the asymmetric reduction of rz,>S-unsaturated iminium salts. 

Surprisingly, acetylation in hot pyridine yields the pyridinium salt 10. The amino group has amidine character and is resistant to diazotization, and condenses only with reactive aldehydes such as formaldehyde and trichloroacetaldehyde.41... 

Other interesting examples of these amino-exchange reactions are the conversion of 3-aminocarbonyl-4-R-l-(2,4-dinitrophenyl)pyridinium salt (2) into 3-aminocarbonyl-4-R-l-cbutylpyridinium salt by Cbutylamine (82RTC342) and the preparation of l-(pentadeuteriophenyl)-3-amino-carbonyl-4-deuteriopyridinium salt from 3-aminocarbonyl-l-(2,4-dinitro-phenyl)-4-deuteriopyridinium salt (2, R = D) with pentadeuterioaniline (84T433) (Scheme IIL2). 

N-Amination of 2-[o-(l,3-dioxolan-l-yl)phenyl]pyridine (121) with O-tosylhydroxylamine gave an A-amino derivative, which underwent ring closure on the action of 70% perchloric acid to yield a pyrido[2,l-a]phthal-azinium salt (122, R = H) (92JHC1049). The 7-hydroxy derivative of a pyrido[2,l-fl]phthalalzinium salt (122, R = OH) was prepared similarly by cyclization of l-amino-2-(o-methoxycarbonylphenyl)pyridinium salt, ob-... 

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. 

Haiyan Lu, Zhuoyi Su, Ling Song, Patrick S. Mariano A Novel Approach to the Synthesis of Amino-Sugars. Routes To Selectively Protected 3-Amino-3-deoxy-aldopentoses Based on Pyridinium Salt Photochemistry, J. Org. Chem. 67,3525-3528 (2002)... 

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