Pd/1,3-双(二苯基膦)丙烷催化苯并噁唑C-2位直接芳基化反应的研究（英文）

Pd/1,3-Bis(diphenylphosphino)propane Catalyzed Arylation of Benzoxazoles at C-2 Position with Aryl Bromides

利用简单商业可得的PdCl2和1,3-双(二苯基膦)丙烷(dppp)作催化剂,高效催化了苯并噁唑和溴苯C-2取代的芳基化反应.该催化体系表现出了很好的官能团容忍性,当催化剂用量为0.1 mol%时,反应6 h收率可达90%以上,更重要的是,当催化剂用量低至0.01 mol%时,通过延长反应时间,转化率仍然能达到90%以上.通过汞中毒实验,透射电镜和X射线光电子能谱证实了该反应是钯纳米粒子催化的过程.此外,通过控制实验证实了底物苯并噁唑在反应过程中经历了开环和关环的途径.最后,通过热过滤和高分辨质谱实验从一定程度上证实了该反应可能经历了Pd(0)-Pd(Ⅱ)的反应历程.

A catalyst system combined of PdCl2 with 1,3-bis(diphenylphosphion)propane (dppp), which was simple and from commercially available materials, was reported for the highly efficient arylation of benzoxazoles at C-2 position with aryl bromides. This catalytic system could tolerate a great number of functional groups in benzoxazole and bromobenzene. With a low PdCl2 loading of 0.01 mol%, aryl bromides could be completely converted into the desired products for 24 h. If the loading of catalyst was up to 0.10 mol%, most of substrates could give more than 90% yields in 6 h. The exploration of the reaction mechanism discovered that Pd nanoparticles were formed during this reaction. The morphology and composition analysis of the Pd nanoparticles with transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) indicated that dppp played a key role to block the aggregation of palladium particles. In addition, the ring-opening pathway of benzoxazoles in the reaction process was proved by control experiments. Hot filtration experimental and high resolution mass spectrum (HRMS) analysis of filtrate suggested that the real active species were Pd(0)-Pd(Ⅱ)/dppp complexes.