Zinc pyridine salt

Quinolinyl moiety has been applied in the Negishi reaction either as an electrophile or as nucleophile. 2- or 4-substituted quinolinyl triflates or bromides have been used extensively for introduction of aromatic rings at the C2 or C4 positions of the heterocycle. In a representative example, Murata et al. employed a Negishi reaction in his effort toward the formal synthesis of antitumor compound camptothecin. In accordance to that, 2-chloropyridine was allowed to react with lithium naphthalenide, followed by zinc chloride, to afford the corresponding zinc pyridine salt. Reaction of the resulting organozinc intermediate with 2-chloro-3-quinoline carboxylate provided the hetero biaryl core of camptothecin. ... 

A number of zinc compounds with organic constituents (e.g., zinc salts of organic acids) have therapeutic uses. These include antidandruff zinc pyridinethione, antifungal zinc undecylenate used to treat athlete s foot, zinc stearate and palmitate (zinc soap), and antibacterial zinc bacitracin. Zinc naphthenate is used as a low-toxicity wood preservative, and zinc phenolsulfonate has insecticidal properties and was once used as an intestinal antiseptic. The inhalation of zinc soaps by infants has been known to cause acute fatal pneumonitis characterized by lung lesions similar to, but more serious than, those caused by talc. Zinc pyridine thione (zinc 2-pyridinethiol-l-oxide) has been shown to cause retinal detachment and blindness in dogs this is an apparently species-specific effect because laboratory tests at the same and even much higher dosages in monkeys and rodents do not show the same effect. 

Five-hundredths mole of a manganese(II), iron(II),t cobalt(II), nickel(II), copper(II), or zinc(II) salt is dissolved in 300 ml. of distilled water containing 20 ml. of pyridine. To this solution is added slowly with stirring a solution of 8.00 g. of ammonium thiocyanate in 100 ml. of distilled water, and the resulting mixture is allowed to stand in an ice bath until precipitation appears complete (ca. an hour). The precipitate is collected on an 8-cm. Buchner funnel and is washed with three 10-ml. portions of an ethanol-pyridine (9 1) solution. The product is air-dried for not longer than 10 minutes. It is powdered and then dried in a desiccator over potassium hydroxide until constant weight has been attained (ca. 24 hours). In the cases of copper(II) and zinc(II), the dipyridine compound is obtained. Details of separate syntheses are given in Table I. 

Synonyms bis(2-pyridylthio)zinc i,i -dioxide bis-(i-hydroxy-2(iH)-pyridinethionato-0,S)zinc De-Squaman Vancide ZP zinc pyridinethione zinc omadine zinc pyridine-2-thiol-i-oxide (T-4)-bis(i-hydroxy-2(iH)-pyridinethionato-0,S) zinc N,N -dioxide bis(2-pyridylthio)zinc bis(i-hydroxy-2(iH)-pyridinethionato)zinc 2-pyridinethiol-i-oxide zinc salt Vancide P 2-mercaptopyridine-i-oxide zinc salt zinc i-hydroxy-2-pyridine-thione omadine zinc OM-1563 pyridinethiol-i-oxide, zinc salt zinc-pyrion zinc i-hydroxypyridine-2-thione zinc 2-mercaptopyridine-N-oxide zinc 2-pyridinethiol-i-oxide zinc polyanemine zinc PT N,N, -dioxide bis(2-pyridylthio) zinc ZNPT pyrithione zinc... 

Pyridine A Oxides. Analgesic and antiinflammatory dmgs niflumic acid [4394-00-7] (68) and pranoprofen [52549-17-4] (69) are manufactured from nicotinic acid N-oxide [2398-81 -4]. The antiulcer dmg omeprazole (66) is produced from 2,3,5-trimethylpyridine N-oxide [74409-42-0]. Zinc pyrithione, the zinc salt of pyrithione (45), is a fungicide derived from 2-chloropyridine N-oxide (45). 

The mechanisms of the electrophilic substitutions in the isoxazole nucleus have not yet been studied. They should not differ fundamentally from those usually accepted for the substitution of aromatic systems but the structural specificity of the isoxazole ring might give rise to some peculiarities, as recently specially discussed.One important point is that isoxazole shows a clearcut tendency to form coordination compounds. Just as pyridine and other azoles, isoxazoles coordinate with halogens and the salts of heavy metals, for example of cadmium,mercury,zinc. Such coordination... 

The reaction between acyl halides and alcohols or phenols is the best general method for the preparation of carboxylic esters. It is believed to proceed by a 8 2 mechanism. As with 10-8, the mechanism can be S l or tetrahedral. Pyridine catalyzes the reaction by the nucleophilic catalysis route (see 10-9). The reaction is of wide scope, and many functional groups do not interfere. A base is frequently added to combine with the HX formed. When aqueous alkali is used, this is called the Schotten-Baumann procedure, but pyridine is also frequently used. Both R and R may be primary, secondary, or tertiary alkyl or aryl. Enolic esters can also be prepared by this method, though C-acylation competes in these cases. In difficult cases, especially with hindered acids or tertiary R, the alkoxide can be used instead of the alcohol. Activated alumina has also been used as a catalyst, for tertiary R. Thallium salts of phenols give very high yields of phenolic esters. Phase-transfer catalysis has been used for hindered phenols. Zinc has been used to couple... 

Associated to copper(II) pre-catalysts, bis(oxazolines) also allowed the asymmetric Diels-Alder and hetero Diels-Alder transformations to be achieved in nearly quantitative yield and high diastereo- and enantioselectivities. Optically active sulfoximines, with their nitrogen-coordinating site located at close proximity to the stereogenic sulfur atom, have also proven their efficiency as copper ligands for these asymmetric cycloadditions. Other precursors for this Lewis acid-catalyzed transformation have been described (e.g., zinc salts, ruthenium derivatives, or rare earth complexes) which, when associated to bis(oxazolines), pyridine-oxazolines or pyridine-bis(oxazolines), led to efficient catalysts. 

The structure of coordination polymers formed with 3,6-bis(pyridin-3-yl)-l,2,4,5-tetrazine and zinc salts can be controlled by the choice of alcoholic solvents. Infinite lattice compounds of the form [Zn2L2(N03)4(Me0H)2(//-L)] and [Zn2(/U-L)3(N03)4](CH2C12)2) have been structurally characterized. The former structure shows an alternating single- and double-bridged species whereas the latter exists as a non-interpenetrated ladder complex.273... 

Reductive dimerization of substituted pyridines to yield bipyridyls by zinc is catalysed by nickel salts under phase-transfer catalytic conditions [25]. 

The one-electron reduction of diquaternary salts of 2,2 -bipyridine has attracted much attention. When an aqueous solution of diquat dibromide (75) is treated with a one-electron reducing agent, such as zinc dust, the solution acquires an intense green color. This is due to the formation of the stable radical cation 87. The one-electron transfer is completely reversed by air. In theory the radical cation 87 can take up another electron to form the neutral species 88. The stability of the radical cation 87 is due to the ability of the odd electron to be located at any of the nuclear positions because of the near coplanarity of the two pyridine rings. The potential 0 of the first one-electron transfer occurs at — 0.35 V in aqueous solution... 

A number of other routes are available for the syntheses of diquaternary salts of 4,4 -bipyridines. One method that has been extensively studied involves reaction of a 1-alkylpyridinium salt with sodium amalgam (or sodium in liquid ammonia) to form the 1,1 -dialkyl-1,1, 4,4 -tetrahydro-bipyridine, which is readily oxidized to the corresponding l,l -dialkyl diquaternary salt. This reaction is analogous to the synthesis of 4,4 -bipyridine by the action of sodium on pyridine, followed by oxidation of the intermediate tetrahydrobipyridine. " The reduction may be achieved electrolytically or by reaction with zinc or magnesium. Various oxidizing agents have been used to assist the conversion to the di-quaternary Another synthesis of diquaternary salts of... 

Dichloro-tetrapyridino-rhodium Chloride, [Rh py4Cl2]Cl, is prepared by dissolving rhodium zinc in aqua-regia, and, after removal of acid, heating the aqueous solution with pyridine. On cooling, the pyridino-salt is deposited in yellow prisms. It melts when heated, yielding a black oil, and on further heating, metallic rhodium. 

The formation of activated iminium intermediates derived from nitrogen heterocycles has been reported by Comins . The activation of pyridine derivative such as 214 with phenyl chloroformate provides the pyridinium salt 215, which smoothly reacts with the zinc homoenolate 216 leading to the addition product 217 in 66% yield . The reaction... 

Copper-zinc reagents add to various pyridinium salts leading either to the 1,2- or to the L4-adduct, depending on the substituent pattern of the pyridine ring (Scheme 95) 2 . ... 

Second, the electroreduction of Co2+ (at —0.86 V/SCE) which is initially irreversible becomes reversible in the presence of zinc salts. Under these conditions, the electrogenerated Co+ species has a life-time estimated at several seconds. Consequently, it is more stable towards the disproportionation reaction than the cobalt species generated in the presence of pyridine used as ligand. 

For ammonia and primary amines there are two possible pathways, but when secondary amines are involved, only the hydrogenolysis pathway is possible. Other reducing agents167 can be used instead of hydrogen and a catalyst, among them zinc and HCI, sodium cyano-borohydride NaBHjCN,168 sodium triacetoxyborohydride,169 sodium borohydride,170 iron pentacarbonyl and alcoholic KOH,171 BH -pyridine,172 and formic acid. When the last is used, the process is called the Wallach reaction. In the particular case where primary or secondary amines are reductively methylated with formaldehyde and formic acid, the method is called the Eschweiler-Clarke procedure. It is possible to use ammonium (or amine) salts of formic acid,173 or formamides, as a substitute for the Wallach conditions. This method is called the Leuckart reaction, and in this case the products obtained are often the N-formyl derivatives of the amines instead of the free amines. Primary and secondary amines can be N-ethylated (e.g., ArNHR —< ArNREt) by treatment with NaBH4 in acetic acid.175... 

Zinc enolates have been shown to react with chiral /V-acylpyridinium salts with high diastereo-selectivity (Scheme 24) (93JOC5035). Other metallo enolates gave products with lower diastereoselectivity. Titanium enolates react with /V-acylpyridinium salts to yield 1,4-dihydropyridines, which on subsequent oxidation (aromatization) give 4-(2-oxoalkyl)pyridines (84TL3297). 

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