Rh/Ag双金属催化的碳氢键氧化Heck反应研究

Rh/Ag Bimetallic Catalyzed C—H Bond Olefination of Benzonitriles

报道了Rh/Ag双金属催化的苯甲腈类底物碳氢键氧化烯基化反应,并合成了一系列苯甲酰胺类衍生物.另外,对反应的机理也做了研究,提出了一个可能的机理.

Transition-metal-catalyzed C—H functionalization emerges as an atom-economical and highly efficient strategy in the synthetic organic chemistry. In this regard, oxidative Heck reaction, pioneered by Fujiwara and Moritani, represents a great evolvement to the traditional Heck reaction by obviating the substrate preactivation. While palladium was routinely adopted as the catalyst of choice because of its well established catalytic activities, other transition metals, especially rhodium also proved to be suitable candidate in pursuit of such oxidative C—H alkenylation because of its low catalyst loading, high efficiency and function group tolerance. Under such circumstance, the Rh（III）-catalyzed oxidative C—H alkenylation has witness a great advancement in the past decade, with many functionalities such as-COOH,-CONHR, CO2 Et, NHAc etc. being explored as suitable directing groups for the initiation of C—H activation. However, most of these directing groups needed prior installation. With our continuing interest in Rh（III）-catalyzed C—H functionalization, herein we would like to present a nitrile based bimetallic Rh/Ag catalyzed C—H alkenylation reaction. In this protocol, nitrile was assumed to transform into imine which then took part into the Rh（III） catalyzed C—H bond olefination reation. With such reaction cascade, a library of ortho-alkenylated benzamides could be directly obtained from benzonitriles in one pot fashion. All the substrates are commercially available and easy to obtain. A general procedure for the bimetallic Rh/Ag catalyzed C—H olefination of benzonitriles： an oven-dried 10 m L Schlenk tube was charged with nitrile 1（If the nitrile was solid, 0.2 mmol）, [Rh Cp＊Cl2]2（6.2 mg, 0.01 mmol）, Ag Sb F6（13.8 mg, 0.04 mmol） in sequence, followed by refilling with N2. Then olefins 2（0.5 mmol）, nitriles 1（If the nitrile was liquid, 0.2 mmol） and Ac OH were added through syringe. After stirring at 120 ℃ for 24 h, the reaction mixture was cooled to room temperature and filtered through a celite plug. The solvent was removed in vacuo and the residue was purified by column chromatography to afford the desired product 3.