钯催化下N-亚硝基导向的芳环上氨基邻位C(sp^2)-H键的直接酰氧基化反应

Palladium-catalyzed N-nitroso-directed ortho C(sp^2)-H acyloxylation of N-alkyl-N-nitrosoarylamines

以醋酸钯为催化剂,通过对芳环sp2碳氢键的活化,实现了一个高区域选择性的芳环上氨基邻位的直接酰氧基化反应.该反应具有良好的官能团兼容性,当苯环上有给电子基或一般吸电子基时反应均可发生.该方法具有反应条件温和、操作简单、条件易于控制、产率较高等优点.对可能的反应机理提出了建议.

Transition metal-catalyzed direct C-H bond functionalization has been used in the construction of a variety of carbon-carbon and carbon-heteroatom bonds with features of step-economics and green chemistry primarily. By this strategy, a series of valuable polyfunctional compounds can be synthesized expediently. The efficient coordination of nitroso to transition metals made this group act as a favorable directing group to carry out the functionalization of inert C-H bond. N-Nitrosoanilines are also a class of very useful medicinal compounds and synthetic materials for the preparation of various nitrogen-containing compounds. In this paper, an efficient and highly regioselective direct ortho-acyloxylation of N-alkyl-N-nitrosoarylamines was developed. Under the catalysis of palladium, by the use of HOAc/Ac20 mixture as the AcO-source and solvent, and PhI（OAc）2 as the oxidant, the reaction gave acyloxylation products on ortho-position of N-alkyl-N-nitrosoarylamines with very high selectivity in moderate to good yields. The reaction conditions were optimized to be N-alkyl-N-nitrosoarylamines mixed with Pd（OAc）2 （10 tool%）, and PhI（OAc）2 in HOAc/Ac20 （1： 1, v/v）, under an air atmosphere at 70~C for 6 h. The reaction can tolerate a series of functional groups such as alkyl, alkoxyl, halogen and ester, etc. The mechanism for the reaction was proposed to be via a five-membered cyclopalladated intermediate which was formed by the coordination of nitroso to palladium, and a Pd（II）/Pd（IV） catalytic cycle was suggested in this transformation. The reaction could proceed under relatively mild reaction conditions, making the method highly applicable.