The oxidative difunctionalization of alkenes is a powerful strategy for the synthesis of various organic compounds. [1] Recent studies have demonstrated that palladium-catalyzed oxidative transformations, such as aminooxygenation, [2] diamination, [3] and dioxygenation [4] of alkenes, can be used efficiently to achieve bond formations at vicinal positions. However, palladium-catalyzed oxidative dicarbonation of alkenes is quite challenging. [5,6] Oxidative cross-coupling of arenes and alkenes using palladium catalysts have been extensively explored. [7] These reactions involve CÀH bond functionalizations to yield the intermediate A, which usually undergoes b-hydride elimination to afford Heck-type products (Scheme 1). Recently, Zhu and co-workers have reported an oxidative intramolecular arylacetoxylation of alkenes in which the C À Pd II bond of intermediate A can be oxidized by PhI(OAc) 2 to form a C À O bond. [8a] This discovery presents an intriguing strategy for the carbonation of alkenes. We postulated that if an additional CÀH bond activation can take place at the palladium center of intermediate A, [9] the highly desired dicarbonation of alkenes could be accom-plished, and would therefore offer a valuable method for constructing two C À C bonds simultaneously (Scheme 1).
The activation of the CÀH bond of acetonitrile has been well-documented by using stoichiometric amounts of a transition metal, [10] such as Rh, [9a-d] Ni, [9e] Ru, [9f,g,i] and Fe, [9j] etc., to yield L n M À CH 2 CN complexes under various reaction conditions. However, in general the catalytic C À H functionalization of acetonitrile by a transition metal is quite rare, [11] and a strong base is generally required. [12] Herein, we report a novel palladium-catalyzed oxidative arylalkylation of alkenes, which involves dual CÀH bond cleavage to form two CÀC bonds in the presence of AgF and PhI(OPiv) 2 . It is worth noting that the rate-determining C sp 3 À H bond activation of CH 3 CN proceeded in the absence of a strong base, and in the presence of acidic additives.
As part of our efforts to develop catalytic fluorination of alkenes, our initial investigation focused on the arylfluorination of 1 a. With the previously reported fluorination conditions involving AgF/PhI(OPiv) 2 , [13] the reaction of 1 a only afforded a small amount of the expected arylfluorination product 2 a (Table 1). Surprisingly, the major product 3 a, having the solvent acetonitrile incorporated, was observed (Table 1, entry 1). Further optimization of the reaction conditions exhibited that a bidentate nitrogen-containing ligand is beneficial to the reaction, and the ligand L4 was shown to give the best yield (entries 2-6). Notably, no reaction occurred in the absence of either the palladium catalyst, AgF, or PhI(OPiv) 2 (entries 7, 8, and 10). The reaction with PhI(OAc) 2 also afforded 3 a but in low yield (entry 9). Other oxidants, such as tert-butyl peroxide, oxone, and benzoquinone, were ineffective (see the Supporting Information). Additional screening of bases showed that AgF was unique for this reaction. No desired product 3 a was observed in the presence of other fluoride and nonfluoride bases, or in the presence of strong bases such as KOtBu and NaN(SiMe 3 ) 2 (entries 11-13). The addition of MgSO 4 is helpful for increasing the yield of 3 a (entry 14). It is remarkable that the reaction is not influenced by acidic additives such as CH 3 CO 2 H or CF 3 CO 2 H (entries 15-16). Furthermore, there was no effect on this transformation when 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO) was employed as a radical scavenger (entry 17).
The scope of substrates was investigated as shown in Schemes 2 and 3. The effect of the protecting group on the nitrogen atom was firstly probed. For the substrates bearing an alkyl or aryl group on N, the reactions proceeded smoothly to provide products 3 a and 3 b in excellent yields. In contrast, the substrates with an electron-withdrawing group on N did not yield the desired products 3 c and 3 d. The position of the substituents on the aryl ring has no significant influence on Scheme 1. Palladium-catalyzed functionalization of alkenes initiated by CÀH bond cleavage.