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.

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Anisole derivatives are important aromatic compounds, their structural motifs are observed in many useful materials, such as pharmaceuticals, natural products, and fluorescent dyes. [1] The development of efficient, selective processes for the synthesis of anisole derivatives is therefore of much interest and importance. Among the most straightforward and atomeconomical routes to anisole derivatives is the C À H alkylation of anisoles with alkenes. However, such C À H bond alkylation approaches for the synthesis of anisole derivatives have met with limited success to date. The Friedel-Crafts reaction of anisoles with alkenes is a well-known route to alkylated anisole derivatives, but such Lewis acid catalyzed alkylation reactions generally suffer from poor regioselectivity and often give a mixture of ortho-and para-regioisomers with the pararegioisomer as the main product, owing to steric and electronic influences. [2][3][4] Recently, the late-transition-metalcatalyzed ortho-CÀH alkylations of various aromatic compounds possessing a directing group have been reported. [5][6][7] However, these late-transition-metal catalysts seemed unsuitable for the ortho-selective C À H alkylation of anisoles, because the interaction between an ether group and the metal center is too weak to regioselectively direct the CÀH bond activation. To the best of our knowledge, the catalytic ortho-selective CÀH alkylation of anisoles with an alkene has not been previously reported.In view of the strong oxophilicity of rare-earth metal ions [8,9] and the high activity of rare-earth alkyl species toward unsaturated CÀC bonds, [10][11][12] we envisioned that the rareearth alkyl complexes might serve as unique catalysts for the ortho-selective CÀH alkylation of anisoles with alkenes. Herein, we report the rare-earth catalyzed CÀH bond addition of anisoles to various olefins, which constitutes the first example of catalytic ortho-selective alkylation of an anisole compound with an alkene.We have recently found that the silylene-linked halfsandwich rare-earth alkyl complexes such as 1 (Figure 1) could serve as unique catalysts for the ortho-selective CÀH silylation of anisoles with hydrosilanes, because the coordination of the methoxy group to the rare-earth metal ion can direct the CÀH activation to selectively take place at the ortho-position. [9] At first, we chose complex 1 as a catalyst to examine the reaction of anisole with styrene and ethylene, but no alkylation product was observed (See Table 1, entry 1). To facilitate the insertion of a C=C double bond into a possible metal-anisyl active species, [9] we then turned to the cationic rare-earth alkyl complexes, which have shown high activity for olefin polymerization. [10,11] To our delight, the cationic half-sandwich scandium alkyl species, generated by the reaction of the half-sandwich scandium dialkyl complex 2-Sc [11f] with an equivalent of [Ph 3 C][B(C 6 F 5 ) 4 ], [13] showed high catalytic activity and selectivity for the ortho-CÀH alkylation of anisole with styrene, which affo...

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