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

Abstract

AbstractFunctionalization of C(sp3)−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 α‐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 α‐branched amines. During the dehydrogenation step of the catalytic cycle, bromobenzene accepts a hydride from the α‐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 Pd0/PdII catalytic cycle, in which oxidative cyclization of a palladium η2‐imine complex generates a three‐membered palladacycle that subsequently undergoes transmetallation reaction with the boroxine.