Matsubara Ryosuke, Yabuta Tatsushi, Md Idros Ubaidah, Hayashi Masahiko, Ema Fumitoshi, Kobori Yasuhiro, Sakata Ken
Department of Chemistry, Graduate School of Science , Kobe University , Nada , Kobe 657-8501 , Japan.
Faculty of Pharmaceutical Sciences , Toho University , Miyama, Funabashi , Chiba 274-8510 , Japan.
J Org Chem. 2018 Aug 17;83(16):9381-9390. doi: 10.1021/acs.joc.8b01306. Epub 2018 Jul 25.
Carbon radicals are reactive species useful in various organic transformations. The C-X bond cleavage of organohalides by photoirradiation is a common method to generate carbon radicals in a controlled fashion. The use of organochloride substrates is still a formidable challenge due to the low reduction potential and the high dissociation energy of the C-Cl bond. In this report, we address these issues by using a nonmetal organic molecule with a relatively simple structure as a photocatalyst. In this catalyst (bis(dimethylamino)carbazole), the amino groups increase both the HOMO and LUMO energy levels, especially in the former. As a result, compared to the parent molecule, the new catalyst shows experimentally red-shifted absorption in the visible region and forms an excited state with better reducing capability. This photocatalyst was used in the reduction of unactivated aryl chlorides and alkyl chlorides in the presence of hydrogen atom donor at room temperature. The catalytic system can also be applied to the coupling of aryl chlorides with electron-rich arene and heteroarenes to affect the C-C bond-forming reactions. Our mechanistic study results support the assumption that carbon radicals are formed from the organochlorides via a single-electron-transfer step.
碳自由基是在各种有机转化中有用的活性物种。通过光照射使有机卤化物的C-X键裂解是一种以可控方式产生碳自由基的常用方法。由于C-Cl键的还原电位低和解离能高，使用有机氯化物底物仍然是一个巨大的挑战。在本报告中，我们通过使用结构相对简单的非金属有机分子作为光催化剂来解决这些问题。在这种催化剂（双（二甲基氨基）咔唑）中，氨基提高了HOMO和LUMO能级，尤其是前者。结果，与母体分子相比，新催化剂在可见光区域表现出实验性的红移吸收，并形成具有更好还原能力的激发态。该光催化剂用于在室温下在氢原子供体存在下还原未活化的芳基氯化物和烷基氯化物。该催化体系还可应用于芳基氯化物与富电子芳烃和杂芳烃的偶联，以实现C-C键形成反应。我们的机理研究结果支持了碳自由基通过单电子转移步骤由有机氯化物形成的假设。
