The coupling of arylboronic acids with electron‐rich allylic bromides is accomplished in the absence of any transition‐metal catalyst through conventional heating. The reaction is completely regioselective, affording only the α‐coupled product, and can be carried out under mild aerobic conditions in an organic solvent; the presence of a base is required.
The preparation of the new ligand 8-(di-tert-butylphosphinooxy) quinoline (1) and the palladium derivatives [PdCl2(1)] (2), [Pd(eta(3)-all)(1)](+) [all = C3H5 (3a), 1-PhC3H4 (3b) and 1,3-Ph2C3H3 (3c)] and [Pd(eta(2)ol)(1)] [ol = dimethyl fumarate (4a) and fumaronitrile (4b)] is reported. The cationic species 3a-3c have been isolated as BF4- salts. The complex 3a(BF4) is obtained either from the reaction of 1 with [Pd(mu-Cl)(eta(3)-C3H5)](2) or from the reaction of ClP(CMe3)(2) with [Pd(eta(3)-C3H5)(8-oxyquinoline)], followed in both cases by chloride abstraction with NaBF4. In the complexes, the ligand 1 is P,N chelated to the central metal, as shown by the X-ray structural analysis of 3a( BF4). At 25 degrees C in solution, 3a(BF4) and 3b(BF4) undergo a fast eta(3) - eta(1) - eta(3) dynamic process which brings about a syn-anti exchange only for the allylic protons cis to phosphorus, while for 4a and 4b a slow rotation of the olefin around its bond axis to palladium takes place. The complexes 2 and 3a(BF4) are efficient catalyst precursors in the coupling of the phenylboronic acid with aryl bromides and chlorides. (C) 2008 Elsevier B. V. All rights reserved
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