Replacing Conventional Carbon Nucleophiles with Electrophiles: Nickel-Catalyzed Reductive Alkylation of Aryl Bromides and Chlorides
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- 作者：Daniel A. Everson ; Brittany A. Jones ; Daniel J. Weix
- 刊名：The Journal of the American Chemical Society
- 出版年：2012
- 出版时间：April 11, 2012
- 年：2012
- 卷：134
- 期：14
- 页码：6146-6159
- 全文大小：683K
- 年卷期：v.134,no.14(April 11, 2012)
- ISSN：1520-5126
文摘
A general method is presented for the synthesis of alkylated arenes by the chemoselective combination of two electrophilic carbons. Under the optimized conditions, a variety of aryl and vinyl bromides are reductively coupled with alkyl bromides in high yields. Under similar conditions, activated aryl chlorides can also be coupled with bromoalkanes. The protocols are highly functional-group tolerant (鈭扥H, 鈭扤HTs, 鈭扥Ac, 鈭扥Ts, 鈭扥Tf, 鈭扖OMe, 鈭扤HBoc, 鈭扤HCbz, 鈭扖N, 鈭扴O2Me), and the reactions are assembled on the benchtop with no special precautions to exclude air or moisture. The reaction displays different chemoselectivity than conventional cross-coupling reactions, such as the Suzuki鈥揗iyaura, Stille, and Hiyama鈥揇enmark reactions. Substrates bearing both an electrophilic and nucleophilic carbon result in selective coupling at the electrophilic carbon (R鈥揦) and no reaction at the nucleophilic carbon (R鈥揫M]) for organoboron (鈭払pin), organotin (鈭扴nMe3), and organosilicon (鈭扴iMe2OH) containing organic halides (X鈥揜鈥揫M]). A Hammett study showed a linear correlation of 蟽 and 蟽(鈭? parameters with the relative rate of reaction of substituted aryl bromides with bromoalkanes. The small 蟻 values for these correlations (1.2鈥?.7) indicate that oxidative addition of the bromoarene is not the turnover-frequency determining step. The rate of reaction has a positive dependence on the concentration of alkyl bromide and catalyst, no dependence upon the amount of zinc (reducing agent), and an inverse dependence upon aryl halide concentration. These results and studies with an organic reductant (TDAE) argue against the intermediacy of organozinc reagents.