【原】无需POCl3氯代，杂环酚羟基直接活化胺基化得到杂环芳胺

由C(Arhet)−OH（与环酰胺互变异构）制备杂环芳胺最常见的方法就是利用POCl3等活化试剂将C(Arhet)−OH的羟基转化为Cl、Br、I、OTf等好离去基团，然后通过SNAr反应得到相应的杂环芳胺。但此方法用到POCl3等高活性试剂，操作繁琐。2020年，云南大学教育部自然资源药物化学重点实验室金毅/林军教授团队开发了一种在Cu催化下，环酰胺直接活化得到杂环芳胺的新方法【Org. Lett. 2020, 22, 16, 6547–6551】。反应利用Cu(acac)2作为催化剂，DTBP作为氧化剂，在DMF中，通过自由基机理实现C-O键的活化胺基化转化。

利用此方法各种脂肪伯胺和脂肪仲胺都可以高产率得到相应产物，除了喹唑啉，吡啶邻位，嘧啶的2/4-位都可顺利反应。

芳环上有给电子基团会降低反应产率，可能原因是富电子环境不利于Cu催化剂的氧化加成。

反应机理

通过机理研究，作者发现N1位氮原子对于此反应至关重要。首先Cu(II)同时与底物的O和N1原子络合得到铜络合物(A)。同时DTBP在Cu(II)催化下均裂生成叔丁氧自由基，其与DMF反应生成胺基甲酰自由基，胺基甲酰自由基与铜络合物(A)反应得到Cu(III)中间体(B)。接着，B还原消除得到胺基甲酸酯(5a)和Cu(I)。Cu(I)对5a进行氧化加成得到Cu(III)络合物(C）。由于脂肪胺的强碱性，发生配体交换得到中间体D，D通过配体交换脱去二甲胺基甲酸得到中间体E。中间体E还原消除得到产物3和Cu(I)。Cu(I)被DTBP氧化实现催化循环。

反应操作

Under air atmosphere, quinazolinone 1 (0.5 mmol), amine 2 (0.6 mmol), DTBP (2.0 mmol, 292 mg), Cu(acac)2 (5 mol%, 6.5 mg) and DMF (5 mL) were added to 10 mL reaction tube. The mixture was stirred at 100 °C in oil bath for 10 h. After cooling to room temperature, the reaction was quenched with saturated NaCl solution and extracted with 30 mL EtOAc for three times. The organic layers were combined, dried over Na2SO4, filtered and evaporated under reduced pressure. The residues were purified by flash column chromatography (FCC) on silica gel to provide the products 3a-3u. The products were further identified by FTIR spectroscopy, NMR spectroscopy, and HRMS.

Under air atmosphere, heterocycle 1 (0.5 mmol), amine 2 (0.6 mmol), DTBP (2.0 mmol, 292 mg), Cu(acac)2 (5 mol%, 6.5 mg) and DMF (5 mL) were added to 10 mL reaction tube. The mixture was stirred at 100 °C in oil bath for 10 h. After cooling to room temperature, the reaction was quenched with saturated NaCl solution and extracted with 30 mL EtOAc for three times. The organic layers were combined, dried S10 over Na2SO4, filtered and evaporated under reduced pressure. The residues were purified by flash column chromatography (FCC) on silica gel to provide the products 4a-4u. The products were further identified by FTIR spectroscopy, NMR spectroscopy, and HRMS.

参考资料

Cu-Catalyzed Direct Amination of Cyclic Amides via C−OH Bond Activation Using DMF；Peng Chen, Kaixiu Luo, Xianglin Yu, Xu Yuan, Xiaoyu Liu, Jun Lin*, and Yi Jin*; Org. Lett. 2020, 22, 16, 6547–6551。