In the presence of manganese chloride (10%), Grignard reagents readily react in THF with aryl bromides, chlorides and even fluorides, as well as aryl methyl ethers bearing in the ortho-or para-position an electron withdrawing activating group (CN, CH=NR, oxazoline). Aryl and N-or S-alkylmagnesium halides have been used successfully. The reaction is performed under mild conditions (0°C to room temperature, 30 minutes to 24 hours) and leads to cross-coupling products in good yields.The transition-metal-catalyzed cross-coupling reactions between an organic halide and an organometallic compound are now a classical tool in organic synthesis. Since the pioneering work of Kharasch, in 1941, 1 these reactions have been extensively studied. 2 In recent years the number of reports has been growing 3 since the search for more efficient and selective C-C bond forming procedures is of great interest for the elaboration of complex molecules. On the other hand, reactions having a larger scope of application were needed for combinatorial chemistry. Many transition metals were used, however, the creation of C-C bonds from alkyl halides is generally performed in the presence of copper salts, 2k,l whereas from aryl and alkenyl halides (Csp 2 -X bond) palladium and nickel complexes are the most common and efficient catalysts. 2c-j Unfortunately, for large scale applications palladium and nickel complexes are expensive and toxic (especially for Ni). These disadvantages are not only related to the nature of the metals but also, in some cases, to the nature of the ligands which are becoming more and more sophisticated. Thus, the discovery of new environmental friendly procedures is of real current interest. In this field, we have recently described the iron-catalyzed alkenylation of Grignard reagents, this reaction is very efficient since even alkenyl chlorides can be successfully used. Moreover, it is performed in the presence of iron acetylacetonate, a non toxic and cheap catalyst. 4 The transitionmetal-catalyzed substitution of aryl halides by an organometallic is also a very challenging area of research. This is especially so for the aryl-aryl coupling which is one of the best ways to obtain biaryls. This important class of products is of great interest because of their numerous applications as polymers, advanced materials (nonlinear optics), liquid crystals, ligands and drugs. 5 Now, we would like to disclose our results about a new manganese-catalyzed cross-coupling reaction between activated aryl halides and Grignard reagents.The preliminary experiments have shown that, in THF, phenylmagnesium bromide quickly reacts with o-chlorobenzonitrile (1a) and the N-phenyl and N-butylimine 1b,c derived from o-chlorobenzaldehyde in the presence of 10% manganese chloride as catalyst. The reactions were carried out between 0 to 20°C and led, within 30 min to 1h, to the corresponding biphenyls 2a-c in good yields (77-88%, Table 1, entries 1 to 3). The coupling product 2d was also obtained in excellent yield from the N-butylimine derived from ...
