Acta Chim. Sinica ›› 2017, Vol. 75 ›› Issue (1): 86-91.DOI: 10.6023/A16070367 Previous Articles     Next Articles

Special Issue: 有机光化学



余晓叶, 周帆, 陈加荣, 肖文精   

  1. 农药与化学生物学教育部重点实验室 华中师范大学化学学院 武汉 430079
  • 投稿日期:2016-07-28 修回日期:2016-09-20 发布日期:2016-09-27
  • 通讯作者: 陈加荣,;Fax:027-67862041
  • 基金资助:

    项目受国家自然科学基金(Nos.21272087,21472058,21472057,and 21232003)和武汉市青年科技晨光计划项目(No.2015070404010180)资助.

Visible Light Photocatalytic N-Radicalbased Intramolecular Hydroamination of Benzamides

Yu Xiaoye, Zhou Fan, Chen Jiarong, Xiao Wenjing   

  1. Key Laboratory of Pesticide & Chemical Biology Ministry of Education and College of Chemistry, Central China Normal University, Wuhan 430079
  • Received:2016-07-28 Revised:2016-09-20 Published:2016-09-27
  • Supported by:

    Project supported by the National Natural Science Foundation of China (Nos. 21272087, 21472058, 21472057, and 21232003), and the Youth Chen-Guang Project of Wuhan (No. 2015070404010180).

The 3,4-dihydroisoquinolinones are a privileged class of heterocyclic motifs and widely found in numerous biologically active compounds. Thus, the development of more efficient and practical methods for their synthesis is highly desirable. Traditional methods are typically focused on transition-metal catalyzed C-H functionalization. Inspired by the recent process of the visible light photocatalytic generation and exploration of N-radicals in organic synthesis, our group in 2014 developed a visible light-induced photocatalytic strategy for direct conversion of the N-H bonds of β,γ-unsaturated hydrazones into N-centred radicals for the first time, and used them in intramolecular radical hydroamination, enabling efficient synthesis of 4,5-dihydropyrazole derivatives. By employing suitable additives or changing reaction parameters, we also successfully achieved highly regioselective 6-endo N-radical cyclization and oxyamination reactions based on N-centred radicals, providing the valuable 1,6-dihydropyradazines, pyrazolines, and pyridazines in good yields. In the hope of extending such N-radical-mediated heterocycle synthesis further, we reported a transition-metal free and visible light photocatalytic N-radical-based intramolecular hydroamination of benzamides. The reaction provides a practical and efficient approach to various biologically important 3,4-dihydroisoquinolinones with generally high yields. Importantly, the continuous flow reaction could significantly shorten the reaction time and still give rise to satisfactory yield. The sunlight irradiation reaction and gram-scale reaction also highlighted the potential synthetic utility of this method. A general procedure for the reaction is as follows:EosinY Na (6.21 mg, 0.009 mmol), NaOH (14.4 mg, 0.36 mmol), amide 1 (0.3 mmol) were dissolved in MeOH (6.0 mL), then, the resulting mixture was degassed via a ‘freeze-pump-thaw’ procedure (3 times). After that, the resulting mixture was stirred at a distance of ca. 5 cm from 3 W blue LEDs (450~460 nm) at room temperature until the starting amides were consumed as monitored by TLC analysis. After concentration in vacuo, the reaction residue was purified by flash chromatography on silica gel[V(petroleum ether)/V(ethyl acetate)=5:1~2:1] directly to give the desired product.

Key words: visible light photocatalysis, N-radicals, hydroamination, N-heterocycles, 3,4-dihydroisoquinolinones