Efficient electrophilic metalation of aromatic C-H bonds leading to new C-C bond formation through regio- and stereoselective addition to alkynes and alkenes has been realized by a catalytic amount (0.02 to 5 mole percent) of palladium(II) or platinum(II) compounds in a mixed solvent containing trifluoroacetic acid at room temperature. Various arenes undergo unexpected selective trans hydroarylation to terminal or internal C&cjs0812;C bonds inter- and intramolecularly with high efficiency (up to a turnover number of 4500 for palladium), especially for electron-rich arenes, giving thermodynamically unfavorable cis-alkenes, and the oxygen- and nitrogen-containing heterocycles. The simplicity, generality, and efficiency of this process should be very attractive to the possible industrial application for the functionalization of arenes.

Efficient trans-hydroarylation of alkynes by simple arenes has been realized regio-and stereoselectively at room temperature in the presence of Pd(II) or Pt(II) catalysts and a mixed solvent containing trifluoroacetic acid (TFA). Various arenes undergo trans-hydroarylation selectively across terminal and internal C-C triple bondssincluding those conjugated to CHO, COMe, CO 2 H, and CO 2 Et groups, affording kinetically controlled cis-arylalkenes predominantly in most cases, especially, in good yields for electron-rich arenes and activated alkynes. The formation of arene/alkyne 1/2 or 2/1 adducts as side products is dependent on the arenes' and alkynes' substituents, which can be suppressed in some cases by changing the catalyst, catalyst concentration, and reaction time. The Pt(II) system, PtCl 2 /2AgOAc/TFA, shows lower catalytic activity than Pd(OAc) 2 /TFA, but higher selectivity, giving higher yields of adducts at the same conversion. On the basis of several isotope experiments and control reactions, a possible mechanism involving electrophilic metalation of aromatic C-H bonds by in-situ-generated cationic Pd(II) and Pt(II) species leading to intermolecular transarylpalladation to alkynes has been discussed.

Formation of unsymmetrical biaryls from simple arenes has been achieVed successfully in a catalytic system of Pd(OAc) 2 /CF 3 CO 2 H(TFA)/K 2 S 2 O 8 just by tuning the concentrations of arenes and TFA under mild conditions. A proposed mechanism containing two-step aromatic C-H actiVation on this noVel intermolecular cross-coupling of arenes is also suggested and partly supported by experiments.

An overview of recent progress in the Fujiwara-Moritani reaction, which is the palladium-catalyzed oxidative coupling of arenes with olefins to afford alkenyl arenes, is described. It is emphasized that regioselectivity on aryl ortho- or meta-CH activation could be controlled very well in the presence of Pd, Rh, or Ru catalysts with the assistance of various chelation groups on aromatic rings in this coupling reaction. Catalytic alkenylation of aryl CH bonds from simple arenes is also discussed, especially from electron-deficient arenes. These advanced protocols would not only make the Fujiwara-Moritani reaction more useful and applicable in organic synthesis but also light the way for the further development of the functionalization of normal CH bonds.

Alkyl spC-H bonds of cycloalkanes and functional branch/linear alkanes have been successfully brominated with KBr using air or O as an oxidant at room temperature to 40 °C. The reactions are carried out in the presence of catalytic NaNO in 37% HCl (aq)/solvent under visible light, combining aerobic oxidations and photochemical radical processes. For various alkane substrates, CFCHOH, CHCl, or CHCl is employed as an organic solvent, respectively, to enhance the efficiency of bromination.