Copper-Catalyzed Coupling of (E)-Bromostilbene with Phenols/Azole: ESI-MS Detection of Intermediates by Using an Ionically-Tagged Ligand

A system based on copper/1,10-phenanthroline efficiently promotes the coupling between phenols or pyrazole with (E)-bromostilbene. (E)-1-Aryloxy-1,2-diphenylethenes were obtained from the coupling with phenols in good to excellent yields (6990%). The exception was the reaction involving a phenol containing an electron-withdrawing cyano group that required a longer reaction time and gave only 49% yield. Kinetic studies indicated the participation of the vinyl halide in the rate-determining step. Under the conditions employed, the activation of the vinyl halide via a radical pathway was discarded using a radical scavenger test. By using an ionically-tagged 1,10-phenanthroline derivative as the ligand, various copper-based ions were detected through ESI(+)-MS. These ions suggested that formation of the active species [phenCuOAr(HOAr)2] precedes the vinyl halide activation.