Pergamon Tetrahedron 54 (1998) 13793-13804 TETRAHEDRON Catalytic alternative of the Ulimann reaction Jwanro Hassan, Vincent Penalva, Laurence Lavenot, Christel Gozzi and Marc Lemaire* Institut de Recherches sur la Catalyse et Laboratoire de Catalyse et Synthrse Organique, CNRS, Universit6 C. Bernard. CPE, B~.t.308, 43 bd. du 11 nov., 69622 Villeurbanne, France Received 8 June 1998; accepted 10 September 1998 Abstract: Symmetrical functionalized biaryls and biheterocyclescould be obtained in good yield via homocouplingof aryl halides by using Pd(OAc)2 as catalyst with base and isopropanol.This alternative of the UIImann reactionhas proved to be compatiblewith sensitivefunctional groups. © 1998Elsevier Science Ltd. All rights reserved. The preparation and utilization of biaryl system is a demanding goal, seeing that biaryls have a large number of physical and chemical properties and can be used as monomers for the synthesis of conductive polymers, l,2,3,4 important biaryl natural products such as steganone,5 supramolecular,6 as ligand catalysts and receptrice macrocyclic moleculesT.There are many methods to prepare symmetrical biaryls, the main way being the UIImann reaction which requires equimolar amounts of copper. 8 Among the other methods, the synthesis of biaryls by arylboronic acid, 9 arylzinc 10 and arylstannanes 11 derivatives were carried out. These methods are effective but need stoichiometric or over stoichiometric amounts of organometallic intermediate. Recently other methods have been developed; the Ni(0)/Zn 12 coupling was used to synthesize bipyridines with good yields but this method also needs an equivalent of nickel and zinc. The nickel-containingcomplex reducing agents NiCRA- bpy was used to synthesize biaryls 13 but an excess of Nail and 2,2'-bipyridine (bpy) were required. Otherwise, a variety of bipyridines and biaryls can be synthesized in moderate to good yields by using the nickel (II) complex 14 furthermore this method is effective for the homocoupling of aryl chlorides. In most cases, an excess of Zinc and Et4NI were required. In contrary, the Pd/formiate 15 coupling in phase transfer catalysis condition requires a catalytic amount of metal but leads to moderate yields and is not compatible with functional g:oups such as aldehyde or nitro which are reduced in similar condition. This paper shows the effectiveness of Pd(OAc)2 as catalyst with base and isopropanol for the direct synthesis of symmetrical biaryls via homocoupling of aryl halides. 16 This catalytic system has been already proved to be efficient for the synthesis of acenaphthylene derivatives,17 as well as in our laboratory for the direct arylation of activated thiophens by iodoaryls.18 In this work, the scope and limitations of the symmetrical coupling reaction (scheme 1) are evaluated by testing a wide variety of aryl halides. R R ~._X Pd(OAc)2 / nBu4NBr ~ ~ Scheme 1 : Homocoupling of aryl halides Fax: 04-72-43-14-08 E-mail: Marc.Lemaire@univ-lyonl.fr 0040-4020/98/$ - see front matter © 1998 Elsevier Science Ltd. All rights reserved. PII: S0040-4020(98)00849-7