Heterocycle arylation

A variety of N-heterocycles can be catalytically phenylated with iodobenzene (Table 4) [11]. This reaction provides substrate scope complementary to that of existing Pd-catalyzed N-heterocycle arylation methods [17]. Both aromatic and non-aromatic heterocycles serve as suitable substrates. Dihydroquinazoline (Table 4,... 

Symmetric and nonsymmetric diarylethenes with various heterocyclic aryl... 

Irie M. Diarylethenes with Heterocyclic Aryl Groups In Crano JC, Guglielmetti RJ, Eds. Organic Photochromic and Thermochromic Compounds. Main Photochromic Families. Vol. Vol. 1. New York Plenum Press, 1999 207-222. 

Gold(I) carbene complexes are readily obtained from heterocyclic aryl ligands 57... 

D Angelo ND, Peterson JJ, Booker SK et al (2006) Effect of microwave heating on Ullmann-type heterocycle-aryl ether synthesis using chloro-heterocycles. Tetrahedron Lett 47 5045-5048... 

A diarylethene with heterocyclic aryl groups has two conformations with the two rings in mirror and C2 symmetries, and the cyclization reaction can proceed only from the C2 symmetry, as shown in Figure 5. The photocyclization is prohibited when the compound is fixed in the mirror symmetry conformation. This means that compounds having special substituents which reversibly fix the conformation undergo gated photochromic reactions (Scheme 4) [17, 18]. 

While the consumption of aniline and other aryl amines in textile dye manufacture has fallen, certain products, particularly aniline, and heterocyclic aryl amines, notably melamine, are produced on a vast scale for use in the manufacture of rubber products and polymers. The growth in demand, and the move from coal to petrochemical feedstocks, stimulated the development of novel manufacturing technologies, particularly continuous vapor- and liquid-phase processes for aniline. 

Heterocyclic aryl amines, such as pyridine and the pyrimidines, are important in the production of colorants and pharmaceutical products and, apart from mention in the relevant sections of this chapter, have received extensive reviews. Here the emphasis is on the industrial applications of aminotriazines, for which industrial interest followed the bulk commercial availability after 1945, particularly from American Cyanamid, of the chlorotriazine cyanuric chloride (182)96. Reactions of cyanuric chloride with amines and substituted amines afford substituted melamines and various aminotriazines that have found application in pharmaceuticals and herbicides. 

A variety of 1-aryl-2-vinylcyclopropanes with a heterocyclic aryl group have been prepared by direct photolysis of the corresponding aryldiazomethanes in the corresponding but-1,3-dienes. All the heteroarylcarbenes employed, viz. pyridylcarbene, furylcarbene and thienylcar-bene, gave low yields (< 15 /o) of cyclopropanes. The main product was the corresponding azine, but minor amounts of stilbene were also obtained. Thus, when 2-furyldiazomethane was irradiated in but-1,3-diene at — 40°C furfuralazine (20c) was isolated in 18% yield, l-(2-furyl)-2-vinylcyclopropane (21c, R = H) was obtained in 8% yield, and 1,2-bis(2-furyl)ethene (22c, R = H) was formed in 0.8 /o yield. ... 

Some heterocyclic aryl halides are very likely to dehalogenate. In the case of oligothiophenes, the halogenation was highly dependent on small changes of the electronic structure of the aryl halide [87]. The side reaction was suppressed by adjusting the basicity of the reaction mixture. In other cases an alternative StiUe protocol was found [88]. 

Potassium-on-alumina or a lamellar K-graphite catalyst promotes total hydrogenation of benzene rings. Carbocyclic and heterocyclic aryl rings are reducible with... 

Electron-Rich Heterocycle Arylation by Aryl Chlorides. 59... 

There are now many reports of palladium-catalyzed five-membered heterocycle arylation by aryl iodides and aryl bromides [26-31], However, only a few reports describe the use of generally cheaper and more accessible aryl chlorides in such reactions. Curiously, the first paper describing aryl chloride use in heterocycle... 

However, a truly general method for electron-rich heterocycle arylation was not reported until 2007 [38], Electron-rich, bulky butyl-di-l-adamantylphosphine or /er/-buty I dicyclohexyl phosphine in combination with Pd(OAc)2 afforded the best results, and the former was chosen because of cost considerations. Interestingly, electron-rich AMieterocyclic carbene ligands that facilitate oxidative addition of aryl chlorides to low-valent transition metals are inefficient in heterocycle arylation. A number of structurally diverse electron-rich heterocycles are reactive (Scheme 3). Thiophene, benzothiophene, 1,2- and 1,3-oxazole derivatives, benzofuran, thiazoles, benzothiazole, 1-alkylimidazoles, 1-alky 1-1,2,4-triazoles, and caffeine can be arylated. Electron-rich, electron-poor, and heteroaryl chlorides can be used. 

Two sets of conditions have been developed for electron-rich heterocycle arylation [94, 95], Most acidic heterocycles such as benzoxazole or benzothiazole may be arylated by employing fBuOLi base, aryl iodide, and DMF solvent (Scheme 23). These reactions proceed at 140 °C in minutes. For less acidic imidazole, 1,2,4-triazole, and caffeine derivatives a stronger fBuOK base is required, and the reaction proceeds by a benzyne-type mechanism. Formation of regioisomer mixtures was observed if substituted aryl halides were used in combination with fBuOK (Scheme 23). 

The mechanism for heterocycle arylation is likely analogous to that postulated with monodentate trialky lphosphine ligands (Scheme 18). The higher reactivity and extended catalyst lifetime observed with bidentate phosphine-alkene ligand might... 

In one additional example of the formation of C-arylglycosides from glycals, Ichikawa, et al.,65 illustrated the applicability of this chemistry to heterocyclic aryl species. Specifically, as shown in Scheme 2.4.15, tri-O-acetoxy glucal was treated with furan and borontrifluoride etherate. The result was a 54% yield of the desired C-furanoglycoside as a 1 1 anomeric mixture. 

Heterocyclic aryl chlorides can be coupled with aryl magnesium chlorides using a Pd(dba)2-dppf catalyst system. Even unactivated aryl tosylates have been successfully coupled with aryl Grignard reagents in the presence of as little as 0.1% of a catalyst prepared from Pd(dba)2 and chelating phosphines of the Josiphos-type. Syrmnetrical biaryls can be prepared from the direct homocoupling of aryl iodides and bromides using a combination of phosphine-free Pd(dba)2 and TBAF in DMF. ... 

Thiapyryl radicals with heterocyclic aryl rings directly bound to the thiapyryl ring... 

A further improvement was the development of ligands 5 and 6, the use of which allowed for the synthesis of tetra-ortho-substituted biaryls, as well as the use of heterocyclic aryl chlorides and heteroarylboronic acids and esters (Equation 2.22) [40]... 

Scheme 15 Domino cyclopropane arylation followed by Suzuki coupling or heterocycle arylation...

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