Sonogashira couplings of aryl bromides

Palladium catalyst supported on poly(4-methylstyrene) can be used for biphasic nonpolar Suzuki and Sonogashira coupling of aryl bromides and chlorides with good product yields. The catalyst can be recycled five times with negligible decrease in the activity. 

Scheme 5.20 Pd-catalyzed carbonylative Sonogashira coupling of aryl bromides...

X.-F. Wu, H. Neumann, M. Beller, Ghent.-Eur. J. 2010, 16, 12104-12107. A general and convenient palladium-catalyzed carbonylative sonogashira coupling of aryl bromides. 

Soheili, A., Albaneze-WaUcer, J., Murry, J. A., Dormer, P. G., and Hughes, D. L. (2003). Efficient and general protocol for the copper-free Sonogashira coupling of aryl bromides at room temperature. Org. Lett., 5, 4191 194. 

Remmele, H., Kollhofer, A. and Plenio, H., Recyclable catalyst with cationic phase tags for the Sonogashira coupling of aryl bromides and aryl chlorides, Organometallics, 2003, 22,4098. 

Bohm, V. P. W., Herrmann, W. A. Coordination chemistry and mechanisms of metal-catalyzed C-C coupling reactions, 13 a copper-free procedure for the palladium-catalyzed Sonogashira reaction of aryl bromides with terminal alkynes at room temperature. Eur. J. Org. Chem. 2000,3679-3681. 

The Sonogashira reaction is usually carried out at about 80 °C. Pd(OAc)2, PdCl2(PPh3)2 or Pd(PPh3)4 are used in the presence of excess amine in most cases. It should be added that these Pd compounds as precursors do not always show the same behavior and sometimes show different activity. At this temperature, decomposition of some labile alkynes tends to occur. Therefore, the reaction should be carried out under milder conditions as far as possible to prevent the side reaction. Pd on charcoal acts as an efficient catalyst for the coupling of aryl bromides such as 3-bromopyridine in the presence of Cul, PPhs, and /-Pr2NH in DMA-H2O [12],... 

The first examples of NHC-Pd complexes applied to the Sonogashira reaction were reported to show a limited scope in the coupling of aryl iodides and activated aryl bromides with acetylene [23,33,52]. However, the use of A-carbamoyl-substituted heterocyclic carbene Pd(ll) complexes expanded the use to alkyl-acetylenes and deactivated aryl iodides and bromides [124] (Scheme 6.40). 

A palladium catalyst with a less electron-rich ligand, 2,2-dipyridyl-methylamine-based palladium complexes (4.2), is effective for coupling of aryl iodides or bromides with terminal alkynes in the presence of pyrrolidine and tetrabutylammonium acetate (TBAB) at 100°C in water.37 However, the reactions were shown to be faster in NMP solvent than in water under the reaction conditions. Palladium-phosphinous acid (POPd) was also reported as an effective catalyst for the Sonogashira cross-coupling reaction of aryl alkynes with aryl iodides, bromides, or chlorides in water (Eq. 4.18).38... 

Sonogashira reaction. The first system consisted in the use of the oxime palladacycles 7a-f at elevated temperatures, without the aid of Cul or an amine base, for the coupling of aryl iodides and bromides. They also reported on the use of complex 48b in aqueous media for the coupling of aryl iodides and bromides and terminal acetylenes in excellent yields. ... 

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