Difluorodiazoethane as a masked acetylene equivalent in formal [3+2] cycloadditions with ketones to access 2,3-functionalized furans

The unusual reactivity of difluorodiazoethane (CF2HCHN2) as masked acetylene equivalent in the transition-metal-free [3 + 2] cycloaddition with beta-ketones is demonstrated. This operationally simple and safe methodology enables a modular synthesis of 2,3-functionalized furans that cannot be accessed otherwise. The reaction features mild conditions, broad substrate scope with good functional group tolerance, and produces diverse 2,3-functionalized furan derivatives in high yields. The practicality and robustness of this reaction are showcased by gram-scale synthesis. DFT calculations provide evidence for the proposed mechanism that involves a base-mediated sequential defluorination, nucleophilic addition, and intramolecular cyclization as the key elemental steps of the reaction.