Copper catalysis halide exchange

While primary electrophiles proved successful, secondary alkyl halides proved troublesome. Alkyl iodides were the most efficient but bromides and chlorides could also be successfully employed by using a catalytic amount of Nal to promote halide exchange. Copper iodide proved to be a beneficial cocatalyst to achieve satisfactory yields. An array of experiments gave the conclusion that the reaction proceeds via in situ formation of the metallated heteroarene, as already suggested for nickel/copper- and copper-catalyzed direct arylation and alkynylation of aromatic heterocycles [44, 52]. It was also suggested that nickel nanoparticles play an important role in the catalysis. 

The coupling of terminal alkynes with aryl or vinyl halides under palladium catalysis is known as the Sonogashira reaction. This catalytic process requires the use of a palladium(0) complex, is performed in the presence of base, and generally uses copper iodide as a co-catalyst. One partner, the aryl or vinyl halide, is the same as in the Stille and Suzuki couplings but the other has hydrogen instead of tin or boron as the metal to be exchanged for palladium. 

Zeolites are very useful catalysts for a large variety of reactions, from acid to base and redox catalysis [27]. Hutchings et al. reported that bis(oxazoline)-modified Cu (II)-HY catalysts are effective for asymmetric carbonyl- and imino-ene reactions and aziridination of styrene [28, 29]. Recently Djakovitch and Kohler [30-34] found that Pd(II)-NaY zeolite activates aryl halides towards Heck olefination, a-arylation of malonate, and amination reactions. It is well known that alkali-exchanged faujasite zeolites are solid base catalysts [35]. Owing to the usefulness of zeolites in organic chemistry, and our interest, we recently reported the use of modified alkali-exchanged zeolite Y, NaY zeolite [36] with electron rich copper catalyst in the Y-arylation of nitrogen heterocycles with aryl halides to afford A -arylheterocycles in excellent yields under mild conditions without the use of any additive. 

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