Ullmann-type Coupling Reaction of Aryl Trifluoromethanesulfonates Catalyzed by Low Valent Nickel Complexest

Abstract

The Ullmann-type homocoupling of aryl sulfonates to biaryls has been studied with the low valent nickel catalysts generated in situ from nickel(II) chloride, triphenylphosphine, sodium iodide, and zinc powder under ultrasounds irradiation in N, N-dimethylformamide. The reactivity of aryl sulfonates examined increased in the following order: methanesulfonate<p-toluensulfonate<trifluoromethanesulfonate. This reaction was compatible with a variety of functionalities such as ketone, ester, amide, and nitrile. Yields dropped with 2-substituted aryl trifluoromethanesulfonates and further to no reaction with 2, 6-disubstituted ones. Irradiation of ultrasounds effectively accelerated the reaction to he able to reduce the reaction time to half in certain cases compared to the ordinary magnetic stirring.