4- phenyl pyridine N- oxide

NaOCl, cat chiral Mn(III)-salen, cat 4-phenyl-pyridine N-oxide (enantioselective)... 

The free-radical arylation of pyridine N-oxides has not been studied systematically, alkylation not at all. When pyridine A-oxide was treated with benzene- and p-chlorobenzenediazonium salts only the 2-arylpyridine jV-oxides were isolated.393 No mention was made of the formation of the 3- and 4-aryl derivatives expected to be produced as well. The phenylation of pyridine N-oxide (diazoaminobenzene at 131° or 181° was found to be the most convenient source of phenyl radicals) was reinvestigated,394 and the reactivities of the nuclear positions found to be in the order 2 > 4 > 3, which is also that predicted6 on the basis of atom localization energy calculations. 2-Phenyl-pyridine N-oxide formed 71-81% of the total phenylation products, whereas the 3-isomer comprised only 5.6-9.6% of that total. The phenylpyridines were found among the by-products of the reaction. 

Tri-substituted alkenes are also good substrates for the metal(salen)-catalysed epoxidation. The addition of 4-phenyl pyridine N-oxide was found to be beneficial in using lower catalytic loadings in industrial applications. This is... 

Substituted pyrimidine N-oxides such as 891 are converted analogously into their corresponding 4-substituted 2-cyano pyrimidines 892 and 4-substituted 6-cya-no pyrimidines 893 [18]. Likewise 2,4-substituted pyrimidine N-oxides 894 afford the 2,4-substituted 6-cyano pyrimidines 895 whereas the 2,6-dimethylpyrimidine-N-oxide 896 gives the 2,6-dimethyl-4-cyanopyrimidine 897 [18, 19] (Scheme 7.6). The 4,5-disubstituted pyridine N-oxides 898 are converted into 2-cyano-4,5-disubsti-tuted pyrimidines 899 and 4,5-disubstituted-6-cyano pyrimidines 900 [19] (Scheme 7.6). Whereas with most of the 4,5-substituents in 898 the 6-cyano pyrimidines 900 are formed nearly exclusively, combination of a 4-methoxy substituent with a 5-methoxy, 5-phenyl, 5-methyl, or 5-halo substituent gives rise to the exclusive formation of the 2-cyanopyrimidines 899 [19] (Scheme 7.6). The chemistry of pyrimidine N-oxides has been reviewed [20]. In the pyrazine series, 3-aminopyrazine N-ox-ide 901 affords, with TCS 14, NaCN, and triethylamine in DMF, 3-amino-2-cyano-pyrazine 902 in 80% yield and 5% amidine 903 [21, 22] which is apparently formed by reaction of the amino group in 902 with DMF in the presence of TCS 14 [23] (Scheme 7.7) (cf. also Section 4.2.2). Other 3-substituted pyrazine N-oxides react with 18 under a variety of conditions, e.g. in the presence of ZnBr2 [22]. 

Bis(difluoromethoxy)phenyl]-2-[5-(2-(l-hydroxy-l-methyl)ethyl) thiazolyl]ethyl pyridine N-oxide... 

The di-pyridinyl derivative of the current invention, (+/—)-4- 2-[3,4-bis (difuoromethoxy)phenyl]-2-[5-(2-(l-hydroxy-l-(6-bromopyridin-3-yl)-2,2,2-trifluoro)-ethyl)thiazolyl]ethyl pyridine N-oxide, (II), has been prepared and is discussed (1). 

Deoxygenation of pyridine N-oxide. Schweizer and O Neill showed that dichlorocarbene generated from a large excess of phenyl(trichloromethyl)mercury deoxygenates pyridine N-oxide to pyridine. The reaction was slow but the yield better than obtained with other dichlorocarbene precursors. 

There are numerous investigations of the reactivity of di- and polyhalo-pyridazines, particularly polyfluoropyridazines. Aminolysis of l-phenyl-4,5-dichloropyridazin-6-one has been studied in detail. In this and other reactions with nucleophiles, the halogen atom at position 4 is substituted preferentially, although a mixture of 4-amino and 5-amino derivatives is formed in the reaction between 4,5-dihalopyridazin-6-ones and ammonia or amines. It has been now firmly established that displacement reactions on 3,6-dichloropyridazine 1-oxide with sulfur nucleophiles take place at position 6 in contrast to nitrogen or oxygen nucleophiles, where the 3-chlorine atom is replaced preferentially. In connection with the previously observed self-condensation of 3-chloro-6-methylpyridazine to a tricyclic product, the reaction between 3,6-dichloropyridazine and pyridine N-oxides was investigated. 3,6-Dichloropyridazine with 2-methylpyridine N-oxide at 100°-110°C affords three compounds (171, 172, and 173). With 2,6-dimethylpyridine N-oxide, an ether (174) is also formed. The isolation of... 

This point of view is supported by the unusually high values of the partial rate factors of the a- and y-positions in the homolytic phenylation of pyridine-N-oxide ) (a 139, 1.5, y 31.2) compared with those of pyridine (a 1.8, /S 1.0, y 1.2). This behavior can in fact be ascribed to the higher stability of the cr-complex which has a nitroxide type structure (4)... 

Phenyl isocyanate is reduced to aniline (62% yield) and N-methylaniline (307o yield). Pyridine N-oxide is reduced to pyridine (100% yield). Aromatic nitro groups are reduced to —NH2. ... 

A variety of other azaaromatic compounds, pteridines [66], pyridazines [67] etc., enter the VNS reactions with the model carbanion of chloromethyl phenyl sulfone or other a-chlorocarbanions. In these reactions azine N-oxides are more active electrophiles than azines themselves. For instance, quinoline fails to enter the VNS reaction with the model carbanion, whereas quinoline N-oxide reacts rather smoothly [68]. Also 3-(chloromethylsulfonyl-amino)pyridine-N-oxide and its quinoline analogue are able to undergo intramolecular VNS reactions [61]. 

Buncel E, Keum SR, Cygler M, Vaiughese Kl, Bimbaum GI (1984) Studies of azo and azoxy dyestuffs. Part 17. Synthesis and stmcture determination of isomeric a and p phenylazoxypyridines, N-oxides and methiodides. A reexamination of the oxidation of phenylazopyridines and X-ray structure analyses of 4-(phenyl-a-azoxy)pyridinium methiodide and 4-(phenyl-p-azoxy)pyridine-N-oxide. Can J Chem 62 1628-1639... 

By determination of the parameters of the spin adduct spectrum it is often possible to identify the nature of the primary trapped radical, or at least to determine the type of radical trapped. Table 1 gives examples of the range of hyperfine coupling constants obtained for a variety of trapped species for the two most commonly used spin traps DMPO (dimethyl-pyridine N-oxide) and PBN (a-phenyl-N-t-butyl nitrone). Care has to be taken, however, because the coupling constants vary with solvent polarity (for example, in water the DMPO adduct of the t-butoxy radical has < (N) = 1.48 and fl(H) = 1.60 mT while in toluene < (N) = 1.3 and fl(H) = 0.75 mT). 

Aryloxenium ions have also been invoked to explain the thermal isomerization of benzisoxazolo[2,3-a]pyridinium tetrafluoroborate (63 R = N02) to 7-nitrobenzofuro[3,2-Z>]pyridine (64). In contrast, under similar conditions the unsubstituted benzisoxazolopyridinium salt (63 R = H), which is formed in high yield (80%) by intramolecular phenylation of N-oxide (62) (Scheme 15), yields only 2-(o-hydroxyphenyl)pyridine (65) (18%) and much tar. The p-nitro-substi-tuent is thought not only to enhance the electrophilicity of the oxenium moiety but also to destabilize the alternative resonance form (61) of the oxenium ion. 

Pyridin-l-oxid wird mit Hefe glatt zum Pyridin reduziert2. Aus Nitroso-benzolen wer-den mitHilfe vonHefen N-Phenyl-hydroxylamine bzw. Aniline4 (z. B.aus4-Nitro-so-phenol 40% d.Th. 4-Amino-phenol) erhalten. 

When acyloxymethyl iodides (10) were treated with PhO- in acetone, the major products were the phenoxymethyl esters (11) resulting from attack at sp- carbon (b), with lesser amounts of the phenyl esters (12), the products of PhO- attack at the C=0 group (a) (Scheme 3). However, when the corresponding acyloxymethyl chlorides (10 Cl instead of I) were treated similarly, attack at only C=0 was observed22 Rate and equilibrium constants were reported for reactions between a series of N-benzoyloxypyridinium salts and pyridine A-oxides and DMAP in MeCN 23... 

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