### 钯催化的2-苯氧基吡啶导向的脱羧酯基化反应研究

1. 中国科学技术大学化学系 合肥微尺度国家研究中心 合肥 230026
• 投稿日期:2019-05-22 发布日期:2019-07-09
• 通讯作者: 王官武 E-mail:gwang@ustc.edu.cn
• 基金资助:

项目受中国科学院战略性先导科技专项（B类）项目（No.XDB20000000）资助.

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

Li Zhong-Yuan, Jing Kun, Li Qi-Li, Wang Guan-Wu

1. Department of Chemistry and Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei 230026
• Received:2019-05-22 Published:2019-07-09
• Contact: 10.6023/A19050190 E-mail:gwang@ustc.edu.cn
• Supported by:

Project supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (No. XDB20000000).

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 using α-oxocarboxylic acids was reported in 2008, a lot of substrates have been employed to synthesize acylated products due to the easily available α-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 mol%), K2S2O8 (1.0 mmol), Ag2CO3 (1.0 mmol), 2 (1.0 mmol), D-CSA (0.125 mmol), and 1,4-dioxane (2.5 mL) in a 25 mL tube was heated at 80℃ for a suitable time. The reaction mixture was cooled to room temperature, and concentrated in vacuo. Purification of the residue by column chromatography on silica gel with petroleum ether and ethyl acetate as the eluent provided the desired product 3.