Stoichiometric metal oxidant applied in the functionalization of indolizine at the 3-position through C–H activation in a previous report was found to increase the cost of the synthesis and worsen the environmental pollution. In this paper, we developed a Pd(OAc)2/O2 catalytic system with or without ligands for an oxidative Suzuki coupling reaction of indolizine at the 3-position through C–H activation. As reported in the literature, some indolizines dimerized when catalyzed by palladium acetate under ligand-free conditions. However, we found that the dimerization of 2,3-unsubstituted indolizines was inhibited by the addition of ligands. Based on this finding, the arylation of these indolizines can be successfully achieved via a Pd(OAc)/O2 system using picolinic acid as a ligand. 1,2-disubstituted indolizines that do not easily dimerize can react smoothly with arylboronic acids under ligand-free conditions. Furthermore, broad group tolerance was shown in both indolizine and arylboronic acid. Finally, this method has the advantages of mild conditions, a broad array of starting materials and the use of a green oxidant.
之前的报告发现,在通过 C-H 活化对
吲哚利嗪进行 3 位官能化反应时,使用的
化学计量
金属氧化剂会增加合成成本并加剧环境污染。本文开发了一种含
配体或不含
配体的 Pd(OAc)2/O2 催化体系,用于通过 C-H 活化进行
吲哚利嗪 3 位的氧化铃木偶联反应。据文献报道,在无
配体条件下,一些
吲嗪类化合物在
醋酸钯催化下会发生二聚反应。然而,我们发现加入
配体后,2,3-未取代的
吲嗪类化合物的二聚化受到了抑制。基于这一发现,我们可以使用
吡啶甲酸作为
配体,通过 Pd(OAc)/O2 系统成功实现这些
吲嗪类化合物的芳基化。在无
配体条件下,不易发生二聚化的 1,2-二取代
吲嗪类化合物能与芳基
硼酸顺利发生反应。此外,
吲哚利嗪和芳基
硼酸都具有广泛的基团耐受性。最后,该方法还具有条件温和、起始材料广泛和使用绿色氧化剂等优点。