Fluoro-Promoted\nThermal Ring Expansion of Cyclopropyl\nCarbenes to <i>gem</i>-Difluorinated Cyclobutenes

Synthesis of <i>gem</i>-difluorinated cyclobutenes\npresents\ncertain challenges for considering the compatibility of the fluorine\natom introduction with four-membered ring retention. Herein, we develop\na transition-metal-free synthetic strategy toward <i>gem</i>-difluorinated cyclobutenes from <i>gem</i>-difluorinated\ncyclopropyl <i>N</i>-tosylhydrazons via ring expansion reaction.\nThe <i>gem</i>-difluoro substitution alters the properties\nof the cyclopropane, facilitating the thermal rearrangement of cyclopropyl\ncarbenes into cyclobutenes. This reaction can be easily handled free\nfrom inert gas protection, thus offering an efficient route to synthesize <i>gem</i>-difluorinated cyclobutenes.