Copper‐Catalyzed Reaction of Trifluoromethylketones with Aldehydes via a Copper Difluoroenolate

A copper‐catalyzed reaction of easily accessible α,α,α‐trifluoromethylketones with various aldehydes affords difluoro‐methylene compounds in the presence of diboron and NaO t Bu. The key process of the reaction is the formation of a copper difluoroenolate by 1,2‐addition of a borylcopper intermediate to α,α,α‐trifluoromethylketones and subsequent β‐fluoride elimination. Mechanistic studies including the isolation and characterization of a possible anionic copper alkoxide intermediate are also described.