Tu, F. Xu, Synthesis , , 49 , Moon, U. Bin Kim, D. Sung, W. Kim, J. Microwave-assisted conditions enabled a simple, rapid, one-pot synthesis of arylaminomethyl acetylenes in very good yields using arylboronic acids, aqueous ammonia, propargyl halides, copper I oxide and water as the solvent within ten minutes. Jiang, S.
Huang, Synlett , , 25 , Gao, Y. Shao, J. Zhu, H. Mao, X. Wang, X. Lv, J. An Expedient Synthesis of Thyroxine D. Evans, J. Katz, T. West, Tetrahedron Letters , , 39 , Zhang, G. Zhang, M. Zhang, J. Cheng, J. Srivastava, D. Yadav, A. Yadav, G. Watal, L. Yadav, Synlett , , 24 , Nasrollahzadeh, A. Ehsani, M. Maham, Synlett , , 25 , Moon, J.
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Nam, K. Rathwell, W. Kim, Org. Huang, T. Shade, A. Hyde, J.
Olsen, C. Merlic, J. New N- and O-arylations with phenylboronic acids and cupric acetate D. Chan, K. Monaco, R.
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He, Q. Chen, Synlett , , A cross-coupling reaction of arylboronic acids with KSCN salt to yield aryl thiocyanates is catalyzed by copper acetate in the presence of 4-methylpyridine serving both as ligand and base under 0.
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Various arylboronic acids were suitable under the reaction conditions. Sun, H. Zhang, W. The details of these general steps remain under debate.
Mechanism of the Chan-Lam Coupling
In particular, how the electrophile is activated and how the C—N bond forms remain somewhat unclear. Initial formation of a Cu-amide complex is supported by the observation that copper I amido complexes react at rates similar to other copper I complexes.
Subsequent reductive elimination generates the product and regenerates the catalyst. EPR spectroscopy experiments  and computational studies  suggest the involvement of copper II complexes in some copper-catalyzed amination reactions. A copper II complex may form after electron transfer from a Cu I -amide complex to the aryl halide Eq. Loss of halide from the resulting radical anion followed by coupling of the aryl radical and copper produces a cationic copper I complex. Subsequent reductive elimination regenerates the catalyst and forms the C—N bond.
Recent developments in copper-catalyzed radical alkylations of electron-rich π-systems
Complicating the picture further, a wealth of evidence suggests that radical intermediates are not involved in copper-catalyzed aminations. For example, substrates containing radical clocks do not undergo rearrangement, and reactions under N 2 with copper I salts are faster than reactions run in air. Copper-catalyzed amination is highly useful for the preparation of aryl amides and N -arylated heterocycles. Although alkenyl electrophiles can be used in some cases, aryl electrophiles are more commonly employed.
Among aryl electrophiles, aryl iodides react most rapidly, followed by aryl bromides and aryl chlorides. Aryl iodides can react selectively in the presence of an aryl bromide Eq. Aryl chlorides and bromides bearing electron-withdrawing groups give the best yields in general, while electron-rich aryl bromides and chlorides react sluggishly Eq.
In many metal-catalyzed cross-coupling reactions, coordination of heteroatoms to the metal center impedes catalysis. Copper catalysts are not as susceptible to this problem as palladium catalysts. In fact, six-membered heterocyclic chlorides are typically more reactive than aryl chlorides and five-membered heterocyclic chlorides despite the coordinatively active lone pair in the former.
For example, 2-chloropyridine and 2-chloropyrimidine both give higher yields of coupling product than chlorobenzene in coupling reactions with benzimidazole Eq.