A highly efficient, site-selective, visible light-accelerated, remote C–H halogenation of unsymmetrical aromatic bisamides/amidoesters has been developed. Unprecedented selectivity was realized in this C–H functionalization reaction. The N,N′-(1,2-phenylene)bisamides/amidoesters, derived from various halogenated acids and aliphatic/aromatic acids, were selectively mono-brominated para to the more electron-deficient group. This unique, site-selective bromination of aromatic amine derivatives proceeded under mild and metal-free conditions, without the use of any oxidant or base. The present procedure benefits from short reaction times, avoids excessive bromination, and is air and moisture tolerant. Furthermore, the synthetic utility of the products has been demonstrated by preparing useful substrates and intermediates, including 2-perfluoroalkyl benzimidazole, para-bromoaniline derivatives and substituted biphenyls. A mechanistic investigation using experimental and theoretical means was undertaken to attempt to explain the observed phenomena. Based on DFT calculations, the mechanism involves the differential formation of nitrogen-centered (amidyl) radicals which leads to the observed regioselectivity. Additionally, when the radical stabilizing abilities of both amides are similar, the regioselectivity breaks down, leading to a mixture of products (2x–2z).

中文翻译：

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氮中心自由基的差异形成导致N，N'-（1,2-亚苯基）双酰胺和2-酰胺基苯酚的空前区域选择性溴化

已经开发出了一种高效的，选择性的，可见光加速的，不对称芳族双酰胺/酰胺基酯的远程C–H卤化方法。在此C–H官能化反应中实现了前所未有的选择性。衍生自各种卤代酸和脂族/芳族酸的N，N '-（1,2-亚苯基）双酰胺/酰胺酯是选择性单溴对位的缺电子的基团。芳香胺衍生物的这种独特的位点选择性溴化反应是在温和且无金属的条件下进行的，无需使用任何氧化剂或碱。本方法得益于反应时间短，避免了过量的溴化并且耐空气和湿气。此外，通过制备有用的底物和中间体（包括2-全氟烷基苯并咪唑，对-溴苯胺衍生物和取代的联苯。使用实验和理论手段进行了机械研究，以试图解释观察到的现象。基于DFT计算，该机理涉及氮中心（（基）自由基的差异形成，这导致观察到的区域选择性。此外，当两种酰胺的自由基稳定能力相似时，区域选择性也会下降，从而导致产物混合（2x–2z）。