Cobalt-Catalyzed C(sp~3)-H Bond Activation To Construct Indoline Skeleton

As an important structural unit,the indolines are prevalent in biologically active molecules,and pharamaceuticals,and natural products,and exhibit unique pharmacological activities.Recently,the synthesis of indolines strategy by transition metal-catalyzed C-H bond functionalization has developed rapidly.Unfortunately,those reaction mainly rely on the noble metal catalysts(such as Ru,Rh,Pd,Ir).Compared with these noble metal catalysts,exploring the earth-abundant cobalt catalyzed C-H bond functionalization is still highly desirable,which might exhibit unique activities,with the additional advantages of being inexpensive and relatively nontoxic.In this paper,a series of organic compounds containing N-O bonds(TsNHOR)was designed and synthesized,and a novel "Co/organic oxidant" catalytic system was developed.A range of indoline derivatives were synthesized via C(sp3)-H bond amidation by using earth-abundant and easy available cobalt salt as the catalyst,N-(2(tert-butyl)phenyl)pyridine amide as the substrate,and the organic compound N(pivaloyloxy)-4-methylbenzenesulfonamide as the oxidant.Furthermore,this protocol features mild conditions,simple steps,and react efficiently.And a series of indoline derivatives were synthesized with 5 mol%catalyst.In addition,the target product could be obtained in 92%yield when the reaction was performed on gram-scale,and the directing group was easily removed under mild conditions,which further demonstrates the application of this protocol.At last,the reaction mechanism was explored by H/D exchange experiment,radical trapping experiment,and kinetic isotope effect experiment,and a plausible reaction mechanism was proposed.Scheme 1...