钯催化的2-苯氧基吡啶导向的脱羧酯基化反应研究  

Palladium-Catalyzed Decarboxylative Coupling of Potassium Oxalate Monoester with 2-Aryloxypyridines

作　　者：李忠原 景昆 李祁利 王官武[1] Li Zhong-Yuan;Jing Kun;Li Qi-Li;Wang Guan-Wu(Department of Chemistry and Hefei National Laboratory for Physical Sciences at the Microscale,University of Science and Technology of China,Hefei 230026)

机构地区：[1]中国科学技术大学化学系合肥微尺度国家研究中心

出　　处：《化学学报》2019年第8期729-734,共6页Acta Chimica Sinica

基　　金：中国科学院战略性先导科技专项(B类)项目(No.XDB20000000)资助~~

摘　　要：发展了一种高效的通过钯催化导向碳?氢键活化的策略在苯环上引入酯基官能团的方法.草酸单乙酯钾盐在过硫酸钾和碳酸银的协同作用下脱羧生成酯基自由基,然后酯基自由基加成到钯环上,最后经过还原消除的过程实现了2-苯氧基吡啶苯环的邻位酯基化.该反应为合成一系列水杨酸乙酯衍生物提供了一种切实有效的途径.Transition metal-catalyzed C—H activation has attracted extensive attention because of its excellent functional group tolerance and high efficiency.Among them,palladium-catalyzed reactions exhibit versatile catalytic cycles and have mild conditions compared to others.Therefore,the palladium-catalyzed C—H activation has been employed broadly as a practical strategy in synthetic chemistry during the past decade.Since the first example of palladium-catalyzed decarboxylative C—H acylation usingα-oxocarboxylic acids was reported in 2008,a lot of substrates have been employed to synthesize acylated products due to the easily availableα-oxocarboxylic acids as well as the importance of acylation.However,the transition metal-catalyzed C—H esterification via decarbonylation is still limited.Our group previously developed the first directed C—H esterification of methyl ketoximes and 2-phenylpyridines by using potassium oxalate monoester as the decarboxylative reagent.Encouraged by this impressive result as well as the importance of salicylate derivatives in drug discovery,herein we disclose the efficient palladium-catalyzed decarboxylative esterification of 2-aryloxpyridines.This reaction proceeds smoothly with potassium oxalate monoester,affording the desired products in moderate to good yields(50%~82%).Compared to our previous work,the electron-donating pyridinyloxy(PyO)group as the directing group and six-membered metallocycle intermediate dramatically enhance the practicability and substrate tolerance of the present method.In addition,one of the products has been chosen as the model compound to deprotect the directing group to get the valuable salicylate derivative.The present method not only provides an efficient and convenient protocol for the synthesis of ethyl salicylate derivatives,but also enriches the diversity of Pd(II)/Pd(IV)catalytic reactions.A general procedure for the esterification of 2-aryloxypyridines 1 with potassium oxalate monoester 2 is as following:a mixture of 1(0.5 mmol),Pd(OAc)2(10 mo

关 键 词：钯催化 碳-氢键活化 2-苯氧基吡啶 脱羧 酯基化 

分 类 号：O62[理学—有机化学]