2 -Phenylpyridines, formation

Ciamician reported the formation of 3-halogenopyridines in low yield from the reaction of pyrryl potassium with chloroform, or bromo-form, in ether. Similar reactions of pyrrole with benzal chloride and methylene iodide gave 3-phenylpyridine and traces of pyridine, respectively. These reactions were later reinvestigated by Alexander... 

Oxazepines are readily decomposed by heat and light and by acids and bases.8 Some of these reactions proceed by hydrolytic opening of the oxazepine ring, as in the formation of 1-benzoylpyrrole (1) from 2-phenyl-l,3-oxazepine and cold dilute hydrochloric acid,12 while others involve valence-tautomeric oxazanorcaradienes, as in the thermal conversion of 2-phenyl-l,3-oxazcpine into 2-phenylpyridin-3-ol (2).12... 

Condensation of ( )-4-phenylbut-3-en-2-one (1) with malononitrile (2) in boiling sodium methoxide/methanol was found to give a mixture of 3-cyano-2-methoxy-6-methyl-4-phenylpyridine (3) and 2,6-dicyano-3-methyl-5-phenylaniline (4). Simple and "obvious" mechanisms were advanced to account for the formation of (3) and (4). 

Hiraki et al.104 have prepared a yellow carbonyl solution in methoxyethanol. Addition of 2-phenylpyridine and related ligands led to the formation of orthometallated monochelates, [Ru(CO)2C1(AB)]2. Addition of further ligands then yielded mononuclear complexes. 

Fu and co-workers have shown that the l-chloro-boracyclohexa-2,4-diene 97 reacts with 4-phenylpyridine at room temperature to provide the />-terphenyl analog 26 in 76% yield as an early example of a borabenzene-pyridine-type complex (Equation 6). The X-ray structure of 26, discussed in Section 7.14.3, shows the three rings not to be coplanar <1997OM1501>. Exposure of the l-chloro-boracyclohexa-2,4-diene 98 to a stabilized carbene results in formation of the complex 29 in 83% yield as an air- and moisture-sensitive colorless powder (Equation 7), crystals of which were grown from toluene the X-ray structure of 29 has been discussed in Section 7.14.3. The use of bulky lithium bases to deprotonate the bis(amido) or bis(alkoxy)boranes 19 allows for the formation of the dianionic 2,2 -diboratabiphenyl derivatives 20 (X = NHPh, OBn), the solid-state structures of which have been discussed (Equation 8) <2006CJC81>. 

The reaction of a lithium alkyl or aryl with dry pyridine involves the formation of a dihydro derivative (103) which, on heating or on being oxidized with molecular oxygen in the cold, furnishes the 2-substituted pyridine 104. Alternatively, 103 may be treated with water to give the 1,2-dihydro derivative which is converted to 104 by oxidation with picric acid (in which case the picrate of 104 is the product isolated) or with chloranil.229 No 4-phenylpyridine could be detected by gas chromatography in the reaction with phenyllithium.230 Support for... 

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. 

With hydrochloric acid 10 28 and 2933 undergo ring contraction in good yield to the 1-amino-3-hydroxypyridinium compounds (35). This reaction involves extrusion of N-l and does not occur with 28. 1-Acylaminopyridinium compounds arise from the bicyclic ketone (32) under the same conditions. A different type of pyridine derivative is obtained by reaction of 10,34 28, or 36 33 with base. Thus 10 gave a mixture of 2- and 6-amino-3-hydroxy-4-methyl-5-phenylpyridine, while 28 gave the former and 36 the latter product. The formation of the pyridines can be accounted for by cyclization of 37 which could be formed via a 0 elimination from the enolide anion (33). 

Tetrafluoro(perfluorophenyl)silicates, M [CgF5SiF4]. obtained by the interaction between trifluoro(perfluorophenyl)silanc and metal fluorides MF (M — K. Cs) or tetramethylam-monium fluoride in nonaqueous acetonitrile or diglyme,are excellent reagents for penta-fluoroarylation with formation of pentafluoro-substituted derivatives of benzene. Thus, the reaction of these salts with nitrosonium and nitronium tetrafluoroborates leads to per-fluoro(nitrosobenzene) (14) and perfluoro(nitrobenzenc)(15), respectively, in quantitative yield. In the case of reaction with perfluoropyridine, perfluoro(4-phenylpyridine) (16) (33% yield) and pentafluorobenzene (.37 % yield) arc formed. Reaction of tetramcthylammonium tetrafluo-ro(perfluorophenyl)silicate with bromine or iodine pentafluoride gives the corresponding bro-mopentafluorobenzene and pentafluoro(tetrafluoroiodo)benzene. ... 

Many types of aromatic substrate are known to undergo a cyclometallation reaction when exposed to alkylpentacar-bonylmanganese complexes under thermal conditions. It is well established that the treatment of ligand appended arenes with alkylmanganesepentacarbonyl complexes can lead to the formation of [C,Y] heterochelates of Mn(CO)4 (Y being a two-electron donor ligand) (Equation 6). For instance, aromatic compounds such as W,W-dimethylbenzyl-amine, alkyl benzyl thioethers, 2-phenylpyridine, acetophenone, benzaldehyde, and diazobenzene can be readily... 

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