[Rh^III(Cp*)]-catalyzed ortho-selective direct C(sp²)-H bond amidation/amination of benzoic acids by N-chlorocarbamates and N-chloromorpholines. A versatile synthesis of functionalized anthranilic acids

A RhIII-catalyzed direct ortho-C-H amidation/amination of benzoic acids with N-chlorocarbamates/N-chloromorpholines was achieved, giving anthranilic acids in up to 85 % yields with excellent ortho-selectivity and functional-group tolerance. Successful benzoic acid aminations were achieved with carbamates bearing various amide groups including NHCO2Me, NHCbz, and NHTroc (Cbz=carbobenzyloxy; Troc=trichloroethylchloroformate), as well as secondary amines, such as morpholines, piperizines, and piperidines, furnishing highly functionalized anthranilic acids. A stoichiometric reaction of a cyclometallated rhodium(III) complex of benzo[h]quinoline with a silver salt of N-chlorocarbamate afforded an amido-rhodium(III) complex, which was isolated and structurally characterized by X-ray crystallography. This finding confirmed that the C-N bond formation results from the cross-coupling of N-chlorocarbamate with the aryl-rhodium(III) complex. Yet, the mechanistic details regarding the C-N bond formation remain unclear; pathways involving 1,2-aryl migration and rhodium(V)- nitrene are plausible. Put an "N" to the ring! Carbamates with amides including NHCO2Me, NHCbz, and NHTroc, as well as secondary amines, such as morpholines, piperdines, and piperizines, were coupled to benzoic acids to furnish functionalized anthranilic acids in up to 85 % yield (see scheme; Boc=tert-butoxycarbonyl; Cbz=carbobenzyloxy; Cp*=pentamethylcyclopentadienyl; Troc=trichloroethylchloroformate). KGaA, Weinheim.