Pyridines phenylpyridines

Conditions (a) 1-5 mol% catalyst, w-CPBA/NMO, -78°C, CH2CI2. (b) 1-5 mol% catalyst, NaOCl, 4-phenylpyridine iV-oxide, 0°C, CH2CI2. (c) 1-5 mol% catalyst, NaOCl, pyridine iV-oxide, 0°C, CH2CI2. (d) Solvent = diethyl ether... 

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... 

The quantitative phenylation of pyridine has been studied by two groups of workers. Dannley and Gregg showed that 2-, 3-, and 4-phenylpyridine are formed in relative amounts 58 28 14 in the phenylation of pyridine with dibenzoyl peroxide, as estimated by infrared spectrophotometry. Hey and his co-workers obtained the ratios shown in Table I for the phenylation of pyridine using four different sources of phenyl radicals. ... 

Pyridine has been phenylated with the following free-radical sources benzenediazonium chloride with aluminum trichloride the Gomberg reaction " phenylhydrazine and metal oxides A -nitroso-acetanilide dibenzoyl peroxide phenylazotriphenylmethane di-phenyliodonium hydroxide and electrolysis of benzoic acid. ° Although 2-phenylpyridine usually accounts for over 50% of the total phenylated product, each of the three phenyl derivatives can be obtained from the reaction by fractional recrystallization of the... 

Relatively few pyridines with substituents other than alkyl groups have so far been examined, and with some of these the reaction has been carried out only in the presence of added solvent. A comparison of the reactivities of these pyridines is therefore difficult. It has, however, been established that the presence of benzoyl groups in the 3- and 4-positions causes a very marked drop in the yields of the corresponding 2,2 -bipyridines. The 3- and 4-benzylpyridines were found to be more reactive but even in the absence of solvent, and in vacuo, 4-benzylpyridine gave only about one-third of the yield of the 2,2 -bipyridine compared with pyridine itself. Ethyl nicotinate in the absence of solvent and under vacuum -- gave a similar yield of biaryl but 4-phenylpyridine was found to be less reactive. 

Phenylpyridine has been prepared in quantity only by heating phenyllithium with pyridine.2 The use of a sealed tube is avoided by replacing the ether with toluene.3... 

From this work the deactivation of pyridine to benzene was estimated as about 107. The partial rate factors for nitration of the 3 position of pyridine and the corresponding pyridinium ion were 101,7-2,5 and 1020 respectively. 2-Phenylpyridine was evaluated as 4.9 x 10"5 times less reactive than benzene. 

The partial rate factor for nitration of pyridine-N-oxide in the 4 position was estimated as 4x 10"6 which is, therefore, close to that found for the 3 position of pyridine, and 2-phenylpyridine-N-oxide was evaluated as 2xl0-4 times less reactive than benzene from rate measurements in 74.7-78.6 wt. % acid at 25 °C. 

Reactions of IrCL/I I2C) with 2-(/>-tolyl)pyridine(ptpy) and 3-methyl-2-phenylpyridine(mppy) gave [Ir(ptpy)2Cl]2 and [Ir(mppy)2Cl]2, respectively.323 Treatment with bpy afforded [Ir (ptpy)2-bpy]Cl and [Ir(mppy)2bpy]Cl. All complexes were characterized by UV-vis, emission spectroscopy, and cyclic voltammetry. 

The donor-acceptor complexes [Ir(/r-dmpz)(CO)(PPh2 0(CH2)2R )]2 exhibit photo-induced electron-transfer rate constants of 1012s—1 and charge recombination rates slower than 2 x 10los-1 when R = pyridine and 4-phenylpyridine.534 Further studies on these complexes revealed that recombination reactions were temperature dependent and slower for the deuterated acceptors.535... 

A variety of transition metal complexes including organometallics was subjected to an ac electrolysis in a simple undivided electrochemical cell, containing only two current-carrying platinum electrodes. The compounds (A) are reduced and oxidized at the same electrode. If the excitation energy of these compounds is smaller than the potential difference of the reduced (A ) and oxidized (A ) forms, back electron transfer may regenerate the complexes in an electronically excited state (A+ + A A + A). Under favorable conditions an electrochemiluminescence (eel) is then observed (A A + hv). A weak eel appeared upon electrolysis o t]jie following complexes Ir(III)-(2-phenylpyridine-C, N ) [Cu(I)(pyridine)i],... 

Mercuration reactions provide a convenient approach to a broad range of arylmercury derivatives.82,83 This approach has been applied to a number of substrates, including phenols, indoles, phenylpyridines, and fV-arylamides.83 The products of these reactions as well as their conditions are summarized in Table 1.84 91 Other examples of such reactions include the mercuration of 2-(2 -naphthyl)pyridine (Equation (251)92 and terephthaldehyde (Equation (26))93 with Hg(OCOCF3)2 and Hg(C104)2, which afford 72 and 73, respectively. 

A number of routes are available for the synthesis of 2,2 -bipyridines where one of the pyridine rings is built up from simpler entities. For example, condensation of 2-(aminomethyl)pyridine (31) with acetaldehyde or acetylene over a silicon-alumina catalyst at 450°C gives 2,2 -bipyridine, ° whereas 2-cyanopyridine reacts with acetylene at 120°C in the presence of a cobalt catalyst to afford 2,2 -bipyridine in 95% yield.2-Acetylpyridine with acrolein and ammonia gives 2,2 -bipyridine in the presence of dehydrating and dehydrogenating catalysts, and related condensations afford substituted 2,2 -bipyridines. ° In a similar vein, condensation of benzaldehyde with 2 mol of 2-acetylpyridine in the presence of ammonia at 250°C affords 2,6-di(2-pyridyl)-4-phenylpyridine, ° and related syntheses of substituted 2,2 6, 2"-terpyridines have been described. Likewise, formaldehyde with two moles of ethyl picolinoylacetate and ammonia, followed by oxidation of the product and hydrolysis and decarboxylation, affords a good... 

The results of some of the many aminations of pyridine and its derivatives that have been carried out appear in Table 14. Yields are quoted where possible but these should not be used for quantitative comparisons as reaction and work up conditions vary widely. 2-Alkylpyridines aminate at the vacant a-position, except when the substituent is very large. 2-f-Butylpyridine does not undergo the Chichibabin reaction, probably because the bulky 2-f-butyl group prevents adsorption on to the sodamide surface. In contrast, 2-phenylpyridine undergoes amination in very good yield. Aminations of 2- and 4-methyl-pyridines do not involve attack on the anhydrobases in aprotic solvents, but some ionization does take place in liquid ammonia. 4-Benzylpyridine forms a carbanion (148) which is only aminated with difficulty by a second mole of sodamide (equation 103). 

The second major class of enamines contains the enamino ketones, made from ammonia or an amine and a 1,3-diketone. By this route the same 1,3-diketone can provide both halves of the resulting pyridine such an example is provided by the synthesis of 5-benzoyl-2-phenylpyridine (444) (54YZ259). As in the case of the crotonates, the first examples of the condensation of an enamino ketone with an a,/ -unsaturated ketone were provided by Knoevenagel and Ruschhaupt (1898CB1025), who prepared the range of 3-acetyldihy-dropyridines (445) to (447). Similarly, Mumm and Bohme obtained the 3-acetyl- and 3-benzoyl-2,6-dimethylpyridines (448) and (449) from ethyl acetylpyruvate (21CB726). 

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