Chemoselective [2+1] Cycloaddition of Difluorocarbene with Conjugated Enynes: Synthesis of Alkenyl Difluorocyclopropenes

The chemoselective [2+1] cycloaddition of difluorocarbene with conjugated enynes has been achieved. Using TMSCF 2 Br as the difluorocarbene precursor in the presence of a catalytic amount of n -Bu 4 N + Br –, the reaction proceeded smoothly in THF at 110 °C, affording a series of alkenyl-substituted difluorocyclopropenes. Subsequently, these products could be hydrolyzed in one pot to furnish the corresponding alkenyl-substituted cyclopropenones.