Pyridine, 2-aryl

Recently, a facile synthesis of substituted 2-aryl pyridine ligands was reported by Lohse et al. [293], DuPont researchers have also successfully synthesized a series of fluorine-substituted Ir complexes based on these same families of ligands using a simplified synthetic approach (Scheme 3.79) [294],... 

More recently, Shen et al. reported on a green and efficient three-component one-pot synthesis of 2-aryl-pyridines with the same starting materials as the Hanztsch reaction, under solvent-, catalyst-, and heat-free conditions. This methodology does... 

Pyridine reacts with lithium alkyls and aryls under rather vigorous conditions (e.g. xylene at 100°C) to afford 2-alkyl- and 2-aryl-pyridines. The reaction proceeds by way of the corresponding dihydropyridines (e.g. 275 or a tautomer), and these may be isolated at lower temperatures. The less reactive Grignard reagents give poorer yields of the same products. 

A 2,4,6-trisubstituted pyridine (5) also results from the reaction of the dianion of 2-methylpropene (4) with two molecules of benzonitrile (Scheme A new route to 2-aryl-pyridines is discussed on p. 273. 

Fusion of the 3-aryl-cyclopent[e][l,2]oxazines (374) at 200—280 °C gives 2-aryl-pyridines (375) in 40—80% yield a plausible mechanism is depicted in Scheme 145. Acid-catalysed ring-opening takes a quite different course, ring-contraction occurring (Scheme 146). ... 

Figure 7.40 Synthesis of fluorinated 2-(aryl)pyridines 111 and iridium complexes 112.

A one-pot, three-component synthesis was reported to give the 2-aryl-pyridines 144 in good to excellent yields under solvent-, catalyst-, and heat-... 

Rhodium-catalyzed direct arylations of 2-aryl pyridines were efficiently accomplished with arylstannanes through chelation-assistance (Scheme 9.3) [14]. This report constitutes an early example of a metal-catalyzed direct arylation with an... 

Ru complexes catalyze the reaction between 2-aryl pyridines and alkenyl esters (Scheme 23.16) [75]. These types of olefins are often only slowly reacting substrates in oxidative Heck (Fujiwara-Moritani) reactions [18] thus, their use in Ru-catalyzed C-H olefinations is a remarkable advance. The shown reaction is overall redox neutral and produces 1 equivalent of alcohol or acid as side product. A variety of heterocyclic directing groups can be employed, and many functional groups are tolerated. However, the olefin scope of the reaction is somewhat limited to alkyl- and aryl-substituted alkenes. 

A remarkably simple two-stage synthesis of 2-aryl-pyridines from cyclo-pentadienes has been reported. The 4a,7a-dihydrocyclopenta[ ][l,2]oxazines (10), available from cyclopentadiene and a-halogeno-ketoximes, at 200 °C undergo successive electrocyclic ring-opening and ring-closure to form the acyl-dihydropyridines (11), which aromatize by loss of acetaldehyde as illustrated in Scheme 2. 

Coordination of palladium with the adjacent pyridine ring is likely to facilitate the acylation of 2-arylpyridines with ct-diketones. In the presence of t-butyl hydroperoxide (TBHP), cleavage of the diketones yields radicals that may allow the formation of intermediates such as (115), which yield the acylated products after reductive elimination. Interestingly the ortfto-aroylation of 2-aryl pyridines may also be achieved using the palladium-catalysed reaction with toluene in the presence of TBHP. Here the mechanism is likely to involve initial benzylation followed by oxidation at the benzylic position to give the acylated product. Acetanilides may also be acylated at the ort/jo-position using toluene and TBHP to yield products such as (116). Here a possible mechanism involves initial formation of a cyclopalladated intermediate followed by reaction with an acyl radical formed by oxidation of the toluene. ... 

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