Pulsed light induced trifluoromethylation of 1,3-dimethoxybenzene: A frequency controls chemoselectivity and chemical yield

Herein, we propose a new control method for photochemical reaction with the frequency of the light source as a parameter. Based on this proposal, we have developed a pulsed light induced trifluoromethylation reaction under the simple reaction condition which combined 1,3-dimethoxybenzene/anthraquinone/CF₃SO₂Na without any other additives, oxidant, and reductant. The yield and regioselectivity were improved and the excess reactions were also suppressed by pulsed light irradiation compared to use of conventional light source. Furthermore, it was found that the reaction yield and chemoselectivity changed with each frequency (length of light ON/OFF time) when only frequency of the pulsed light was varied from 1.4 x 10^-5 Hz (a period of 2 h on time and 18 h off time) to 10⁵ Hz (a period of 1µs on time and 9 µs off time) while total irradiation time were fixed at 7200s for all reactions. The result shows that the pulsed light has the potential to control photochemical reactions and that the light irradiation method can be an important factor for the photochemical reaction in addition to conventional factor such as reagents, solution concentration, and temperature.