A photoinduced, FeX3-catalyzed, stereo- and regio-selective halofunctionalization of olefins with MXn via a radical-polar crossover reaction

The classical reaction for the halofunctionalization of olefins involves hazardous and highly toxic molecular halogens. The goal of chemists is to establish green, inherently safe, highly efficient and sustainable synthetic methods. Here, we report a green approach for the halofunctionalization of alkenes with MXn and FeX3, as well as a nucleophile at room temperature under visible-light irradiation in AcOH/CH3CN, without strong oxidants and any ligand. This procedure provides a wide substrate scope and excellent functional-group tolerance, ranging from alkenes and conjugated dienes to medicinally active fragments. The reaction results in good to excellent yields, such as 82% and 84% for the bromoalcoholization and chlorobromination of cyclohexene, respectively. The method exhibits high stereoselectivity, regioselectivity and chemoselectivity, and mechanistic studies support the hypothesis that the reaction is a cascade process based on radical-polar crossover species, supported by DFT calculations. The classical reaction for the halofunctionalization of olefins involves hazardous and highly toxic molecular halogens. Here, the authors report the FeX3-catalyzed halofunctionalization of alkenes with MXn at room temperature, under visible-light irradiation, and without strong oxidants.