Visible-Light-Induced Benzylic C—H Oxygenation Reaction Using Tetrabutylammonium Tribromide as the Catalyst

Abstract

The direct oxidative functionalization of the benzylic C-H bonds of alkyl arenes paves a way for the quick synthesis of carbonyl compounds, which is of great significance in organic synthesis. In the past decades, the photooxidative pathways to achieve this reaction have developed rapidly, using relatively green and readily available oxygen as the terminal oxidant under light irradiation. In this paper, a commercially available and inexpensive chemical reagent, tetrabutylammonium tribromide (TBATB), was used to catalyze the photooxidation of the benzylic C-H bonds. Under visible light irradiation and air atmosphere, a catalytic amount of TBATB was utilized to achieve the efficient conversion of alkyl arenes to the corresponding aryl ketones. The reaction is feasible under mild conditions and without any additives, leading to a broad scope of ketone substrates. This method can be an effective supplement to the current benzylic photooxidation reaction systems.

Bromine radical-enhanced HAT activity leading to stoichiometric couplings of methylarenes with acid chlorides

“…2 It is worth noting that about 25% of the top-selling pharmaceuticals contain a stable benzyl group. 3 Recently, a series of effective strategies have been developed for the direct activation of methylarenes, such as oxidative insertion of transition-metal catalysts, 4 single-electron-transfer (SET) oxidation 5 and hydrogen atom transfer (HAT). 6 Despite significant progress, the direct construction of value-added products through benzylic C–H functionalization from readily available alkylarenes remains an active target among synthetic investigations.…”