Shi Shicheng, Lalancette Roger, Szostak Roman, Szostak Michal
Department of Chemistry, Rutgers University, 73 Warren Street, Newark, NJ, 07102, USA.
Department of Chemistry, Wroclaw University, 14 F. Joliot-Curie Street, Wroclaw, 50-383, Poland.
Chemistry. 2016 Aug 16;22(34):11949-53. doi: 10.1002/chem.201602717. Epub 2016 Jul 15.
Samarium(II) iodide enables a wide range of highly chemoselective umpolung radical transformations proceeding by electron transfer to carbonyl groups; however, cyclizations of important nitrogen-containing precursors have proven limited due to their prohibitive redox potential. Herein, we report the first reductive cyclizations of unactivated cyclic imides onto N-tethered olefins using SmI2 /H2 O. This new umpolung protocol leads to the rapid synthesis of nitrogen-containing heterocycles that are of particular significance as precursors to pharmaceutical pharmacophores and numerous classes of alkaloids. The reaction conditions tolerate a wide range of functional groups. Excellent chemoselectivity is observed in the cyclization over amide and ester functional groups. Such unconventional reactivity has important implications for the design and optimization of new bond-forming reactions by umpolung radical processes. The reaction advances the SmI2 cyclization platform to the challenging unactivated N-tethered acyl-type radical precursors to access nitrogen-containing architectures.
碘化钐（II）能实现多种高度化学选择性的极性翻转自由基转化，这些转化通过向羰基进行电子转移来进行；然而，重要的含氮前体的环化反应由于其过高的氧化还原电位而受到限制。在此，我们报道了首次使用SmI₂/H₂O将未活化的环状酰亚胺还原环化到N-连接的烯烃上。这种新的极性翻转方法能够快速合成含氮杂环，这些杂环作为药物药效基团和众多生物碱类别的前体具有特别重要的意义。反应条件能耐受多种官能团。在环化反应中，相对于酰胺和酯官能团观察到了优异的化学选择性。这种非常规的反应性对于通过极性翻转自由基过程设计和优化新的成键反应具有重要意义。该反应将SmI₂环化平台推进到具有挑战性的未活化N-连接的酰基型自由基前体，以构建含氮结构。
