Key Laboratory of Green Chemistry & Technology, Ministry of Education, College of Chemistry, Sichuan University, Chengdu 610064, China.
Department of Chemistry, University of California, Berkeley, California 94720, United States.
J Am Chem Soc. 2020 Apr 29;142(17):7715-7720. doi: 10.1021/jacs.0c00283. Epub 2020 Apr 21.
We report here the first example of cross-coupling between two different and unactivated C(aryl)-O bonds with chromium catalysis. The combination of a low-cost Cr(II) salt, 4,4'-di--butyl-2,2'-dipyridyl (dtbpy) as the ligand, and magnesium as the reductant shows high reactivity in promoting the reductive cross-coupling of aryl methyl ether derivatives with aryl esters by cleavage and coupling of two different C(aryl)-O bonds under mild conditions. The formation of active low-valent Cr species by reduction of CrCl with Mg can be considered, which prefers to initially activate the C(aryl)-O bond of phenyl methyl ether with the chelation help of dtbpy and an -imine auxiliary. The subsequent consecutive reduction, second C(aryl)-O activation, and reductive elimination allow for the achievement of selective cross-coupling of C(aryl)-O/C(aryl)-O bonds.
我们在这里报告了首例通过铬催化实现两个不同且未活化的 C(芳基)-O 键之间交叉偶联的例子。廉价的 Cr(II)盐 4,4'-二--丁基-2,2'-联吡啶(dtbpy)与镁作为还原剂的组合，在温和条件下通过裂解和偶联两个不同的 C(芳基)-O 键，表现出促进芳基甲基醚衍生物与芳基酯还原交叉偶联的高反应性。可以认为，CrCl 与 Mg 的还原形成了活性低价 Cr 物种，该物种通过 dtbpy 和 -imine 辅助物的螯合作用，优先初始激活苯甲基醚的 C(芳基)-O 键。随后的连续还原、第二次 C(芳基)-O 活化和还原消除，使得 C(芳基)-O/C(芳基)-O 键的选择性交叉偶联得以实现。
