Metal-Free Radical Vicinal Dihalogenation of Olefins Enabled by Synergetic Photocatalytic Energy Transfer and Halogen-Atom Transfer

Vicinal dihaloalkane is extremely important structural unit, and dihalogenation of alkene provides a prospective way access to such moiety. Despite more than a century of development, it is still challenging and necessary to avoid the use of toxic and harmful halogenating reagents and to develop more efficient, sustainable, and broader functional group tolerant and skeleton-compatible strategies. We report herein the first metal-free protocol for radical vicinal dichlorination and dibromination by a photocatalytic energy transfer strategy using N-halo-benzophenonimine (NXB) as the readily accessible halogenating reagents. This approach undergoes the radical addition of a halogen atom derived from the N-X bond photolysis of NXB onto olefins, followed by a halogen-atom transfer process. This approach features facile operation, mild reaction conditions, a wide of functional group tolerance, and is compatible with a large of complex scaffolds such as unsaturated fatty acid, terpenes steroid, alkaloid, sugar, amino acid, and peptide.