Fluorinated biphenyls from aromatic arylations with pentafluorobenzenediazonium and related cations. Competition between arylation and azo coupling
作者:Dmitry Kosynkin、T. Michael Bockman、Jay K. Kochi
DOI:10.1039/a701745f
日期:——
High yields of the mixed perfluorinated biaryls (C6F5–Ar) are obtained by the catalytic dediazoniation of the pentafluorobenzenediazonium salt (C6F5N2+BF4–) in acetonitrile solutions containing various aromatic substrates (ArH) together with small amounts of iodide salts. Activated (electron-rich) as well as deactivated (electron-poor) arenes are successfully pentafluorophenylated by this method. The arylation is distinct from the azo coupling of the same substrates, which takes place in the absence of the iodide catalyst and yields the corresponding diazene (C6F5NN–Ar) as product. The catalytic role of iodide, and the isomeric product distributions obtained with this procedure indicate that the arylation proceeds via the pentafluorophenyl radical in a efficient homolytic chain process. Since azo coupling involves electrophilic aromatic substitution of electron-rich ArH by C6F5N2+, the two competing pathways are distinct and do not have reactive intermediates in common.
通过催化脱重氮化反应,在含有各种芳香族底物(ArH)及少量碘化盐的乙腈溶液中,五氟苯重氮盐(C6F5N2+BF4–)能够高效生成混合全氟联苯(C6F5–Ar),产率较高。无论是活化的(电子富集的)还是去活化的(电子贫乏的)芳香族化合物,都能通过此方法成功实现五氟苯基化。这种芳基化反应与同种底物的偶氮耦合反应截然不同,后者在无碘催化剂存在下进行,产物为相应重氮烯(C6F5NN–Ar)。碘化物在催化中的作用以及由此过程获得的不同异构产物分布表明,芳基化反应是通过高效的均裂链式过程,经由五氟苯基自由基进行的。由于偶氮耦合涉及电子富集的ArH通过亲电芳香取代反应与C6F5N2+的结合,这两种竞争路径是不同的,且没有共同的反应中间体。