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

Vicinal dihaloalkanes are extremely important structural units, and dihalogenation of alkenes provides a prospective way to access such moieties. Despite more than a century of development, it is still challenging and necessary to avoid the use of toxic and harmful halogenating reagents and develop more efficient, broader, functional group-tolerant, and skeleton-compatible strategies. We report herein the metal-free protocol for radical vicinal dichlorination and dibromination of olefins by a photocatalytic energy transfer strategy using N- halo-benzophenonimine (NXB) as the readily accessible halogenating reagent. This approach undergoes 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, and wide functional group tolerance and is compatible with a large number of complex scaffolds such as unsaturated fatty acids, terpene steroids, alkaloids, sugars, amino acids, and peptides.