An organic photoredox catalyst promoted para-selective C–H amination of aryl oximes

Abstract

Direct C–H amination methods are essential because of the importance of aryl amine derivatives. Despite significant progress in transformation methods of a C–H bond to C–N bonds, a general route for para-selective C–H amination remains elusive. This manuscript reports a new method for para-selective C–H amination of aryl oximes through transient steric control. A preliminary mechanism study revealed an interaction between 2,4,6-triphenylpyrylium tetrafluoroborate (TPT) and oxime to form an active aromatic ring. Meanwhile, TPT sterically hindered the ortho, and meta-position C–H bonds, leading to a selective reaction of the pyrazole radical with the phenyl ring at a less hindered para-position, providing a new direction to achieve the para-selective C–H functionalizations.