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

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.