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 (69–90%). 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.