α-C-H Arylation of N-Sulfonyl Amines by Dual Palladium Catalysis

Functionalization of C(sp(3))-H bonds adjacent to a nitrogen atom is an efficient means of preparing structurally complex amines and has long been of interest to synthetic chemists. Herein, dual palladium catalysis is used to achieve a-C-H arylation of linear N-sulfonyl amines with aryl boroxines, rather than N-arylation (C-N bond formation). This method has a broad scope with respect to both the amine and the boroxine, providing convenient access to a-branched amines. During the dehydrogenation step of the catalytic cycle, bromobenzene accepts a hydride from the a-carbon on the amine, producing an imine that subsequently undergoes Pd-catalyzed C-arylation with the boroxine. Mechanistic studies revealed that imine arylation proceeds through an unusual Pd-0/Pd-II catalytic cycle, in which oxidative cyclization of a palladium ?(2)-imine complex generates a three-membered palladacycle that subsequently undergoes transmetallation reaction with the boroxine.

Automated summary

Functionalization of C(sp(3))-H bonds adjacent to a nitrogen atom using dual palladium catalysis provides access to α-branched amines with a broad scope. Mechanistic studies reveal an unusual Pd-0/Pd-II catalytic cycle involving oxidative cyclization and transmetallation.