◊ M.Z. and M.L. contributed equally to this work.
Abstract
Benzylic sp3 C–H bonds have been successfully brominated with potassium bromide by using Oxone
as an oxidant in water/dichloromethane under visible light at room temperature. Toluene,
ethylbenzene and other alkylbenzenes bearing an electron-withdrawing group, such as
Br, Cl, COMe, CO2Et, CO2H, CN or NO2, provide the corresponding benzylic monobromides in good to excellent yields in this
reaction. Dibromides can also be produced in the presence of excess potassium bromide
in a prolonged reaction time. Control of the illuminance of visible light (~500 lux)
is crucial to achieving both high yield and high selectivity in these brominations.
Mono- and difluorides can be conveniently prepared through nucleophilic substitutions
of the benzylic bromides with potassium fluoride.
Key words
benzylic C–H bond - bromination - oxidation - photochemistry - room temperature
