Benzylic C(sp³)-H Azidation: Copper vs Iron Catalysis

The generation of benzylic radicals through hydrogen atom abstraction (HAT) has been a recent research focus and various C(sp(3))-H bond functionalization protocols have been developed relying on this elementary step. We report herein copper- and iron-catalyzed C(sp(3))-H benzylic azidation reactions using mCPBA and NFSI as oxidant, respectively, and TMSN3 as azide source. The reaction is thought to be initiated via intermolecular abstraction of benzylic hydrogen by the in situ generated heteroatom-centered radicals. The Fe(OTf)(3)-catalyzed azidation protocol displays good chemoselectivity as it takes place preferentially at the secondary and tertiary benzylic C(sp(3))-H bonds over the primary benzylic and tertiary aliphatic carbons. Efforts on the development of catalytic enantioselective processes are also documented.