Palladium-catalyzed Oxidative-Heck Reaction, Ortho-C-H Activation And Aromatic Electrophilic Substitution

In this thesis, cyclopalladated ferrocenylimine was successfully applied to oxidative-Heck reaction of arylboronic acids with olefins. Moreover, palladium catalyzed halogenation and ortho-acetoxylation of 2-arylbenzoxazoles were investigated. In addition, cyclopalladated ferrocenylimine-catalyzed bromination of 2-arylbenzoxazoles and subsequent borylation of the brominated products were also explored.?Cyclopalladated ferrocenylimine-catalyzed oxidative-Heck reaction1 An applicable and efficient oxidative-Heck reaction catalyzed by cyclopalladated ferrocenylimine I under base- and ligand-free conditions has been described, and the desired products were obtained with moderate to good yields. The catalytic system employed oxygen as the environmentally benign oxidant and could tolerate various functional groups. This protocol afforded a facile route for the synthesis of substituted olefins (Scheme 1). R1=Ar, COOCnH2n+1 (n= 2,4,8), COC2H5, Yields:mostly 47-99% Scheme 1?Palladium-catalyzed functionalization of 2-arylbenzoxazoles via C-H activation2 With Pd(OAc)2 as the catalyst and PhI(OAc)2 as the oxidant, ortho-acetoxylation of 2-arylbenzoxazoles was studied, affording the desired products bearing various substituents in moderate to high yield. All the new compounds were characterized by HR-MS,1H NMR and 13C NMR. The definite structure of the acetoxylated products was confirmed by 2D NMR spectra (Scheme 2). R= H, o-Me, m-Me, p-Me, m-MeO, Yields:62-84% m,p-(MeO)2 Scheme 23 An efficient and facile protocol for palladium-catalyzed chlorination of 2-arylbenzoxazoles with NCS as the chlorinating reagent has been developed. The catalytic system could tolerate various halogen atoms, such as F, Cl or Br, affording the corresponding products in moderate to excellent yields. The chlorination took place at the para-position of the nitrogen atom in the benzene ring of benzoxazole, which could be determined by HMBC (1H-detected heteronuclear multiple bond correlation) spectra (Scheme 3). R= H, o-Me, m-Me, p-Me, m-F, m-Cl, Yields:70-92% m-Br, p-F, p-Cl, p-Br, o,p-Cl2 Scheme 34 An efficient and facile protocol for bromination has been developed using the cyclopalladated ferrocenylimine I as the catalyst. The bromination took place at the para-position of the nitrogen atom in the benzene ring of benzoxazole, which could be determined by HMBC spectra. The catalytic system could tolerate various functional groups and the desired products were obtained in moderate to high yields (Scheme 4). R= H, o-Me, m-Me, p-Me, Yields:66-92% Scheme 45 A novel and highly regioselective chlorination of 2-arylbenzoxazoles catalyzed by cyclopalladated ferrocenylimine?was developed. The chlorination employed the NCS as the chlorinating reagent, and could proceed smoothly to afford the chlorinated products in moderate to high yields (Scheme 5). Scheme 56 A novel and facile protocol for bromination and subsequent borylation of 2-arylbenzoxazoles has been investigated using cyclopalladated ferrocenylimines?and?as the catalysts. The borylation step could be carried out successively only after removal of the solvent, affording the arylboronic esters in moderate to good yields. This catalytic system provides a new pathway for the synthesis of arylboronic esters containing benzoxazoles moiety (Scheme 6). p-Cl, o,p-Cl2 Yields:62-89% When R= m-Br, p-Br, the diborylation took palce. Scheme 6...