Mechanistic Study of Chemoselectivity in Ni-Catalyzed Coupling Reactions between Azoles and Aryl Carboxylates
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- 作者：Qianqian Lu ; Haizhu Yu ; Yao Fu
- 刊名：Journal of the American Chemical Society
- 出版年：2014
- 出版时间：June 11, 2014
- 年：2014
- 卷：136
- 期：23
- 页码：8252-8260
- 全文大小：641K
- 年卷期：v.136,no.23(June 11, 2014)
- ISSN：1520-5126
文摘
Itami et al. recently reported the C鈥揙 electrophile-controlled chemoselectivity of Ni-catalyzed coupling reactions between azoles and esters: the decarbonylative C鈥揌 coupling product was generated with the aryl ester substrates, while C鈥揌/C鈥揙 coupling product was generated with the phenol derivative substrates (such as phenyl pivalate). With the aid of DFT calculations (M06L/6-311+G(2d,p)-SDD//B3LYP/6-31G(d)-LANL2DZ), the present study systematically investigated the mechanism of the aforementioned chemoselective reactions. The decarbonylative C鈥揌 coupling mechanism involves oxidative addition of C(acyl)鈥揙 bond, base-promoted C鈥揌 activation of azole, CO migration, and reductive elimination steps (C鈥揌/Decar mechanism). This mechanism is partially different from Itami鈥檚 previous proposal (Decar/C鈥揌 mechanism) because the C鈥揌 activation step is unlikely to occur after the CO migration step. Meanwhile, C鈥揌/C鈥揙 coupling reaction proceeds through oxidative addition of C(phenyl)鈥揙 bond, base-promoted C鈥揌 activation, and reductive elimination steps. It was found that the C鈥揙 electrophile significantly influences the overall energy demand of the decarbonylative C鈥揌 coupling mechanism, because the rate-determining step (i.e., CO migration) is sensitive to the steric effect of the acyl substituent. In contrast, in the C鈥揌/C鈥揙 coupling mechanism, the release of the carboxylates occurs before the rate-determining step (i.e., base-promoted C鈥揌 activation), and thus the overall energy demand is almost independent of the acyl substituent. Accordingly, the decarbonylative C鈥揌 coupling product is favored for less-bulky group substituted C鈥揙 electrophiles (such as aryl ester), while C鈥揌/C鈥揙 coupling product is predominant for bulky group substituted C鈥揙 electrophiles (such as phenyl pivalate).