Pd-Catalyzed Fluorocarbonylation of Iodoarenes with Difluoromethyl Benzoates

Palladium-catalyzed fluorocarbonylation of iodoarenes using difluoromethyl benzoate (DFBz) or difluoromethyl <i>p</i>-cyano-benzoate (DFBz-CN) as a fluorocarbonylation reagent has been developed, affording structurally diverse acyl fluorides as products. Both DFBz and DFBz-CN reagents are conveniently prepared through insertion of difluorocarbene into the O-H bonds of carboxylic acids. The activation of these two difluoromethyl benzoates with CsF generates formyl fluoride (HCOF), which readily decomposes into CO and HF. Therefore, both DFBz and DFBz-CN can be successfully used as safe surrogates of CO. This study provides not only a new synthetic method for fluorocarbonylation but also intriguing insights into the different reactivity between the previously known trifluoromethyl benzoate (TFBz, an effective CF₃O^- synthon) and the currently studied difluoromethyl benzoate (DFBz, not a satisfactory HCF₂O^- synthon).