An efficient catalytic system has been developed for the synthesis of benzocyclobutenes by C-H activation of methyl groups. The optimal conditions employed a combination of Pd(OAc) 2 and P ( t )Bu 3 as catalyst, K 2CO 3 as the base, and DMF as solvent. A variety of substituted BCB were obtained under these conditions with yields in the 44-92% range, including molecules that are hardly accessible by other methods. The reaction was found limited to substrates bearing a quaternary benzylic carbon, but benzocyclobutenes bearing a tertiary benzylic carbon could be obtained indirectly from diesters by decarboxylation. Reaction substrates bearing a small substituent para to bromine gave an unexpected regioisomer that likely arose from a 1,4-palladium migration process. The formation of this "abnormal" regioisomer could be suppressed by introducing a larger subsituent para to bromine. DFT(B3PW91) calculations on the reaction of 2-bromo-tert-butylbenzene with Pd(P ( t )Bu 3) with different bases (acetate, bicarbonate, carbonate) showed the critical influence of the coordination mode of the base to induce both an easy C-H activation and to allow for a pathway for 1,4-palladium migration. Carbonate is shown to be more efficient than the two other bases because it can abstract the proton easily and at the same time maintain kappa (1)-coordination without extensive electronic reorganization.

The synthesis of an ionic liquid-supported olefin metathesis catalyst derived from Grubb's ruthenium carbene complex is described. This new supported catalyst has been used in BMI.PF6 solvent, and this allowed success in solving the challenging problem of catalyst recycling. The IL catalyst in BMI.PF6 can be recovered and reused up to 10 consecutive cycles in RCM reactions of several dienes with excellent conversions. Moreover, the IL catalyst shows a remarkable stability in BMI.PF6 and can be stored several months without loss of activity. These results clearly demonstrate the importance of anchoring an imidazolium ionic liquid pattern to the catalyst to avoid its leaching from the BMI.PF6 phase.

Several imidazolinium salts are synthesized from (L)-valine. A study of the structure relationships is achieved to obtain high diastereomeric interactions with an anionic substrate. High splitting up to 60 Hz of the (rac)-potassium Mosher's salt are observed by NMR spectroscopy.

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Biphasic BMI[middle dot]PF(6)/toluene solvent is a remarkably suitable and clean medium for performing olefin metathesis with a new 2nd generation ionic liquid supported-ruthenium catalyst: high levels of recyclability and reusability combined with a high reactivity were obtained with a variety of di- or tri-substituted and/or oxygen-containing dienes, and very low residual ruthenium levels were detected (1 to 22 ppm) in the products.

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Recognition. -Several imidazolium salts are synthesized from (L)-valine. It is found that the choice of counter anion is crucial for the properties of the salt. For example, NTf2 anion leads to room temperature ionic liquids, while the PF6 anion only gives solid salts. -(CLAVIER, H.; BOULANGER, L.; AUDIC, N.; TOUPET, L.; MAUDUIT*, M.; GUILLEMIN*, J.-C.; Chem. Commun. (Cambridge) 2004, 10, 1224-1225; Inst. Chim., CNRS, Univ. Rennes, F-35042 Rennes, Fr.; Eng.) -M. Paetzel 40-128

New perfluoroalkylated polystyrene resins have been prepared by the suspension polymerisation of 4-(perfluoro-n-octyl)styrene. The evaluation of these highly fluorinated insoluble materials as catalyst supports for rhodium-catalysed hydrogenation of styrene and palladium-mediated Suzuki-Miyaura carbon-carbon bond forming reactions with 4-bromo-A C H T U N G T R E N N U N G acetophenone and 4-bromoanisole revealed improvements in the recycling of the perfluoroalkylated catalysts as compared to that achieved using fluorous reverse-phase silica gel.