Cobalt-Catalyzed Cross-Dehydrogenative Coupling Arylation And Amination Assisted By Bidentate Directing Groups

Cross-dehydrogenative coupling?CDC?reactions have become one of the most straightforward protocols in the C-H bond functionalizations.As an important subset of C-H functionalization processes,CDC reactions are attractive because this strategy do not require prefunctionized starting materials,relying instead on oxidative activation followed by net loss of two hydrogen atoms.Despite the tremendous achievements have been achieved in the last decade,unfortunately,CDC reactions have mainly been restricted to precious metal catalysts?rhodium,palladium,etc.?.In this dissertation,the cobalt-catalyzed CDC arylation and amination assisted by 8-aminoquinoline directing group have been studied.The main contents are as follows:1.Cobalt-catalyzed CDC arylationA mixed directing-group strategy for commercially available Co?acac?₃ catalyzed intermolecular CDC arylation of unactivated arenes has been disclosed.Under the cobalt catalysis,different aromatics were identified by the difference of monodentate and bidentate directing group.Two different pathways,namely,a single-electron-transfer process?8-aminoquinoline-directed?and a concerted metalation–deprotonation process?pyridine-directed?,were involved to activate two different inert aromatic C-H bonds.The resulting hexahedral high valence metal intermediates could form functionalized biaryls by reductive elimination.This strategy enables the arylation of a wide range of benzamide and arylpyridines effectively to afford novel bifunctionalized biaryls.Moreover,the aryl radicals have been trapped by 2,6-di-tert-butyl-4-methylphenol to form benzylated products.2.Cobalt-catalyzed CDC aminationAs a powerful synthetic tool for the formation of aromatic C-N bonds,the reported transition-metalcatalyzed direct C-H amination has been ineffective for the synthesis of triarylamines for a long time.Herein,an elegant strategy for the preparation of triarylamines was achieved by double sequent cross-dehydro-coupling amination.It is noteworthy that unactivated arenes and simple anilines were employed as the starting materials with good functional group tolerance.The sterically congested triarylamines,which are difficult to achieve by traditional methods,were also compatible with the transformation.In addition,an organometallic Co???species was isolated and identified by X-ray crystallography,which could deliver triarylamine products by reductive elimination.