“…Unlike its precursor, fluorosulfonyldifluoroacetic acid, which has also been utilized as a difluorocarbene source for conversions of acids to their difluoromethyl esters and alcohols and phenols to their difluoromethyl ethers, TFDA releases difluorocarbene in a controlled, acid-free environment that appears to be essential for high yield additions of difluorocarbene to alkenes. Indeed, TFDA been shown to be useful for adding CF 2 : to a wide variety of alkenes and alkynes, including very electron-deficient alkenes such as α,β-unsaturated esters. ,− However, in a very recent paper Chen and Xu report that TFDA is surprisingly not effective in the direct difluorocyclopropanation of α,β-unsaturated aromatic aldehydes and ketones. , Thus, they describe an indirect approach to accomplish this task, a process proceeding via the addition of difluorocarbene to the respective acetals or ketals.…”