Aryl bromides arylation

Pd2(DBA)3/BINAP system (DBA = dibenzylideneacetone BINAP = 2,2-bis(diphenyl-phosphanyl)-l,1-binaphthyl). Best results were obtained using electron-deficient aryl bromides. Aryl chlorides of any type, however, failed to react under these conditions. The aryl-aziridine coupling reaction could also be carried out with arylboronic acids using a copper catalyst (Scheme 55) <2003JOC2045>. 

PdCI2(dppf) Pd-catalyzed coupling reactions to give polymer-bound aryl bromides. Aryl zinc [96]... 

The order of reactivity of the aryl electrophiles in Pd-catalyzed cyanation is as follows aryl iodides > aryl triflates > aryl bromides > aryl chlorides. The lower the reactivity of the... 

Alkenyl ethers Biaryl iodide Aryl bromides Aryl triflates... 

Aryl triflates, aryl bromides, aryl iodides... 

We then examined the reactions of a variety of aiyl halides with aiylboronic acids containing both electron donating and electron attracting substituents, Table VI. As can be seen from the data contained in Table VI, the reaction appears to be insensitive to the substituents on the boronic acid. However, the reaction is most efficient when aryl iodides are used as the co-reactant. In fact the reactivity trend aiyl iodide > aryl bromide > aryl chloride > aryl fluoride parallels the trend observed in Suzuki reactions carried out thermally, both in solution and on alumina. 

Low yields were obtained in the absence of pivalic acid however, employing greater than 30% pivalic acid did not further improve yields or reactivity. Substrates that performed well included C3-substituted benzothiophenes, C2-substituted thiophenes, pyrroles, imidazole, triazole, imidazopyridine, thiazole, and oxazoles, which could be efficiently arylated with aryl bromides. Unfortunately, benzofuran produced low yields (29% with 2-bromotoluene), and furans encountered issues with diarylation, which could be minimized by using more sterically hindered aryl bromides. Arylation of indolizines could be achieved, albeit electron-deficient aryl bromides required longer reaction times (16-24 h). Heterocyclic aryl bromides, such as 3-bromopyridine, could also be employed with thiazole. Problematic aryl halides included cyano, nitro, acetyl, pyridyl functionalities, and N-heterocyclic V-oxides. Other coupling partners, such as aryl tri-flates and aryl chlorides, performed poorly under the reaction conditions. Unsuitable heterocycles included unprotected imidazoles, 2-aminothiazole, isoxazole, benzothiazole, and benzoxa-zole, which failed to produce arylated products. 

Hydrogen autotransfer has been shown to tolerate a wide range of functional groups, including esters, ethers, tertiary amines, aryl chlorides, aryl bromides, aryl iodides, ketals, nitroarenes, nitriles, and oxetanes. Notably, Williams reported a series of amine alleviations with alcohols in the presence of boronic esters which could be present in either the alcohol or amine starting material (Scheme 12.9). °... 

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