化学学报 ›› 2017, Vol. 75 ›› Issue (1): 74-79.DOI: 10.6023/A16090492 上一篇    下一篇

所属专题: 有机光化学

研究通讯

可见光氧化还原催化下α-酮酸对对位亚甲基醌(p-QMs)脱羧/1,6-共轭加成反应

吴自俊, 汪舰   

  1. 清华大学药学院 北京 100084
  • 投稿日期:2016-09-15 修回日期:2016-11-27 发布日期:2016-12-05
  • 通讯作者: 汪舰,E-mail:wangjain2012@tsinghua.edu.cn;Tel:010-62772583 E-mail:wangjain2012@tsinghua.edu.cn
  • 基金资助:

    项目受国家自然科学基金(No.21672121)资助.

Decarboxylative 1,6-Conjugate Addition of α-Keto Acids with para-Quinone Methides Enabled by Photoredox Catalysis

Wu Zijun, Wang Jian   

  1. School of Pharmaceutical Sciences, Tsinghua University, Beijing 100084
  • Received:2016-09-15 Revised:2016-11-27 Published:2016-12-05
  • Supported by:

    Project supported by the National Natural Science Foundation of China (No. 21672121).

研究了可见光照射下,Ir[dF(CF3)ppy]2(dtbbpy)PF6催化α-酮酸脱羧后得到的酰基自由基与对位亚甲基醌(p-QMs)发生1,6-共轭加成反应,以71%~94%的收率实现了24种不同结构的α-芳基-α,α'-二芳基酮的合成.该反应对于不同电性及立体结构取代的α-酮酸和对位亚甲基醌(p-QMs)都具有较好普适性.该合成策略使用简单易得、具有较好稳定性的α-酮酸为起始原料,以及清洁、廉价且可再生的可见光这一绿色能源,反应还具有条件温和,官能团兼容性好等特点.

关键词: 可见光, 光氧化还原催化, 对位亚甲基醌, 1,6-共轭加成, 自由基

α-Arylated and α,α'-diarylated carbonyls are an important class of building blocks and widely found in biologically active natural and unnatural molecules. The most popular approach to access α-arylated and α,α'-diarylated carbonyls involves transition-metal-catalyzed cross-coupling reactions and metal-free coupling reactions, which always request harsh conditions or high catalytic loading. Visible-light photoredox catalysis, a novel and green catalytic strategy, has recently received increasing attention from chemists and been widely applied to organic synthesis in the past years. Inspired by the recent process of the visible light photocatalytic generation and exploration of α-keto acids as the precursor for acyl radical in decarboxylative cou-pling reactions and 1,4-Michael addition reactions, we found that, however, expand their utilization in more complex systems, such as 1,6-conjugate addition with electron deficient olefins, remains underdeveloped, particularly due to the difficult to design the appropriate substrate, and the harsh conditions often required for metal-catalyzed redox neutral decarboxylation. Here, we report a photoredox catalytic C-C bond formation reaction that enabled by visible-light. The versatility of this protocol has been portrayed by using a wide range of stable and easily accessible aromatic α-keto acids as well as p-QMs. This synthetic strategy also offers access to 24 kinds of different α-keto-α,α'-diarylated ketones in moderate to excellent yields under mild conditions. A representative procedure for the reaction is as follows:2-oxo-2-phenylacetic acid 1a (0.10 mmol), the p-QM (2,6-di-tert-butyl-4-(4-methoxybenzylidene) cyclohexa-2,5-dien-1-one) 2a (0.12 mmol), photocatalyst Ir[dF(CF3)PPy]2(dtbbpy)PF6 (0.001 mmol) and K2HPO4 (0.12 mmol) were dissolved in DCM (1 mL). Then, the resulting mixture was degassed and refilled with N2 via ‘freeze-pump-thaw’ procedure (3 times). After that, the solution was stirred at a distance of ca. 5 cm from a 36 W blue LEDs at room temperature for about 12 h with TLC monitoring. Upon completion of the reaction, the crude product was purified by flash chromatography on silica gel (hexane/ethyl acetate) to give the desired product 3.

Key words: visible light, photoredox catalysis, para-quinone methides, 1,6-conjugate addition, radical