化学学报 ›› 2023, Vol. 81 ›› Issue (2): 111-115.DOI: 10.6023/A22120490 上一篇    下一篇

研究通讯

可见光促进(氮杂)芳香胺与重氮乙酸乙酯的N-烷基化反应

赵亚婷a,b,c, 刘帆c, 汪秋安a,*(), 夏吾炯c,*()   

  1. a 湖南大学化学化工学院 长沙 410000
    b 衢州学院化学与材料工程学院 衢州 324000
    c 哈尔滨工业大学(深圳)理学院 深圳 518055
  • 投稿日期:2022-12-07 发布日期:2023-01-11
  • 通讯作者: 汪秋安, 夏吾炯
  • 基金资助:
    国家自然科学基金(21901141); 衢州学院科研启动基金(BSYJ201714)

Visible-Light-Promoted N-Alkylation Reactions of (aza)Aromatic Amines with Ethyl Diazoacetate

Yating Zhaoa,b,c, Fan Liuc, Qiuan Wanga(), Wujiong Xiac()   

  1. a College of Chemistry and Chemical Engineering, Hunan University, Changsha 410000
    b College of Chemical and Material Engineering, Quzhou University, Quzhou 324000
    c School of Science, Harbin Institute of Technology (Shenzhen), Shenzhen 518055
  • Received:2022-12-07 Published:2023-01-11
  • Contact: Qiuan Wang, Wujiong Xia
  • Supported by:
    National Natural Science Foundation of China(21901141); Start-up Funds of Quzhou University(BSYJ201714)

本工作利用可见光催化剂和Lewis酸双催化体系, 在可见光条件下实现了重氮乙酸乙酯与苯胺衍生物或氮杂芳烃的N-烷基化反应, 合成了一系列α-氨基酸类化合物. 该反应条件温和, 有良好的官能团兼容性和底物普适性. 机理验证实验证明该反应涉及了自由基机理, 由重氮烷在光催化剂作用下通过proton-coupled electron transfer (PCET)过程形成了烷基自由基, 并在Lewis酸催化作用下与胺发生自由基偶联反应形成N-烷基化产物. 这种新的催化机制进一步丰富了重氮化合物在可见光化学反应中的应用类型与范围.

关键词: 可见光, 重氮化合物, 自由基, N-烷基化

Unnatural α-amino acid derivatives are greatly important in pharmaceuticals and biochemicals owing to their diverse biological activities, and usually serve as versatile building blocks in organic synthesis as well. A variety of approaches have been developed to prepare α-amino acid derivatives, among which N—H insertion reactions of diazo compounds are considered to be one of the most direct methods. These N—H insertion reactions typically proceed through carbene active intermediates that derived from diazo compounds by UV-induction or metal catalysis. As a green and powerful avenue to organic synthesis, visible-light-mediated methodology has also been applied to N—H insertion of diazo compounds principally through carbene intermediates. Due to the single reaction mechanism of these reactions, however, the scope of diazo compounds were limited to α-aryl diazoacetates that can directly absorb the visible-light. Therefore, exploring new activation modes is conducive to expanding the applicable scope and reaction type of diazo compounds in visible- light-mediated reactions. Herein we report visible-light-promoted N-alkylation reactions of (aza)aromatic amines with ethyl diazoacetate based on the mechanism of proton-coupled electron transfer (PCET). A series of α-amino acid derivatives were synthesized by the combination of photocatalyst and Lewis-acid catalyst. This method featured in mild reaction conditions, good functional group tolerance and wide range of substrate scope. Mechanism experiments indicated the reaction involved in radical intermediate rather than carbene that engaged in conventional N—H insertion reactions. According to the fluorescence quenching experiment, the alkyl radical intermediate was formed by the PCET step between ethyl diazoacetate and excited photocatalyst. And then radicals cross-coupling occurred under the coordination of Lewis-acid to produce the final N-alkylation products. This new catalytic strategy expands the applications of diazo compounds in visible-light chemical reactions. The general procedure for the visible-light-promoted N-alkylation reactions of (aza)aromatic amines with ethyl diazoacetate is as following: Aniline 1a (0.1 mmol), ethyl diazoacetate 2 (0.2 mmol), Fe(OTf)2 (0.02 mmol) and photocatalyst [Ir(ppy)2(NCMe)2]PF6 (0.005 mmol) were dissolved in MeOH (2 mL). Then the mixture was degassed via a “freeze-pump-thaw” procedure (3 times). After that, the resulting mixture was stirred under irradiation of 30 W blue LEDs at room temperature. Upon reaction completion, the crude product was purified by flash chromatograph on silica gel to give the final product.

Key words: visible-light, diazo compound, radical, N-alkylation