Advances and developments in transition metal-free benzylic C(sp)-H activation/functionalization reactions.

Transition metal-free C(sp)-H activation of toluene derivatives is known as a green and sustainable methodology for constructing carbon-carbon and carbon-heteroatom bonds. Benzylic C(sp)-H activation/functionalization bond formation can be carried out in the presence of organic/inorganic peroxides, bases, acids, and other radical initiators. These radical transformations also occur under photochemical and electrochemical conditions. In this review, we highlight the C-H activation/annulation or C-H activation/functionalization reactions of benzylic carbon atoms in the presence of non-metal catalysts or promoters or without any catalyst.