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Preparation of Unsymmetrical Biaryls via Palladium-CatalyzedCoupling Reaction of Aryl Halides.-The palladium-catalyzed cross-coupling reaction of aryl iodides containing electron-donating substituents (I) with aryl bromides bearing electron-withdrawing groups (II) represents a novel synthetic access to unsymmetrical biaryls (III). A wide range of p-, m-or o-substituted aryl halides can be used. The unsymmetrical biaryls are obtained in high GC yields (mainly 85-100%, except the coupling of o-substituted aryl bromides to naphthyl iodide), but their separation from excess aryl bromide and homocoupling products is very difficult. The selective formation of unsymmetrical biaryls is probably a result of the different reactivities of the aryl halides, but the mechanism is not clear. First examples for the coupling of hetaryl bromides (V) with iodobenzene are presented. -(HASSAN, JWANRO; HATHROUBI,

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