Aryl

In organic chemistry, aryl halides are aromatic compounds in which one or more hydrogen atoms directly bonded to the aromatic ring are replaced by halogens. Aryl halides differ from alkyl halides because of their many differences in their preparation methods and properties. In general, aryl halides (C₆H₅X or ArX, where X = F, Cl, Br, and I) are much less active than simple alkyl halides since they usually do not undergo simple nucleophilic nucleophiles substitution.

Applications

• Amidation reaction: The combination of air-stable CuI and 1,2-diamine ligands in the presence of K₃PO₄ or K₂CO₃ makes it possible for N-amidation of aryl, heteroaryl iodides, bromides and even unactivated aryl chlorides. The best results are achieved by using inexpensive and air-stable copper (I) iodide and N,N'-dimethylated 1,2-diamine ligand as precatalyst. In some cases, other 1,2-diamine ligands including ethylenediamine and 1,2-cyclohexanediamine can be used as very inexpensive ligands substitution. And this reaction can be used for intermolecular amidation of aryl chlorides. Although functionalized aryl chlorides provide lower yields of the desired N-aryl amides, the amidation reactions are already performed at temperatures that are significantly lower than that of amidation of aryl chlorides in the very few cases that are reported previously.

  Fig.1. Amidation of aryl halides

• Coupling reaction: Palladium-catalyzed coupling has become the main method for forming aromatic carbon-heteroatom bonds. The synthesis of arylamines and aryl ethers from aryl halides has undergone significant development. One of the catalytic systems based on the coupling of aryl halides and sulfonates with thiols using CyPF-t-Bu ligands has been reported. The reactions catalyzed by palladium catalysts occur in excellent yields with a wide scope and exhibit extraordinary turnover numbers and high functional tolerances. In addition, aryl tosylate can also react with alkane thiols to form aryl sulfides.

  Fig.2. Coupling of aryl halides

• Cyanation reaction: A method for the cyanation of aryl halides using potassium hexacyanoferrate as a cyanide source has been reported. The advantages of this coupling agent are obvious: potassium hexacyanoferrate is less poisonous than other cyanating agents and can be handled without special precautions. Due to the slow release of cyanide ions, catalyst productivity is significantly improved compared to previously known methods.

Fig.3. Cyanation of aryl halides

References

1. Klapars A, Huang X, Buchwald S L. A general and efficient copper catalyst for the amidation of aryl halides[J]. Journal of the American Chemical Society, 2002, 124(25): 7421-7428.
2. Fernández-Rodríguez M A, Shen Q, Hartwig J F. A general and long-lived catalyst for the palladium-catalyzed coupling of aryl halides with thiols[J]. Journal of the American Chemical Society, 2006, 128(7): 2180-2181.
3. Schareina T, Zapf A, Beller M. Potassium hexacyanoferrate (II)—a new cyanating agent for the palladium-catalyzed cyanation of aryl halides[J]. Chemical Communications, 2004 (12): 1388-1389.