Direct Access to Trifluoromethylated Benzo[d]oxepines from o‑Alkynylaryl Aldehydes and Trifluorodiazoethane

Reported in this Letter is a silver-catalyzed reaction between -alkynylaryl aldehydes and trifluorodiazoethane that enables an expedient synthesis of trifluoromethylated benzo[]oxepines. The reaction works through a silver-promoted 6-- cyclization of -alkynylbenzaldehydes for the generation of an isochromenylium intermediate, which upon a ring-expansive addition of trifluorodiazoethane delivers a novel class of trifluoromethylated benzoxepine frameworks. This strategy was applied to the synthesis of phosphonylated benzo[]oxepines using the Seyferth-Gilbert reagent.