Copper(I)-Catalyzed [4 + 1] Cycloaddition of Silyl Dienol Ethers with Sodium Bromodifluoroacetate: Access to β,β-Difluorocyclopentanone Derivatives

Silyl dienol ethers readily underwent copper(I)-catalyzed [4 + 1] cycloaddition with sodium bromodifluoroacetate to afford 4,4-difluorocyclopent-1-en-1-yl silyl ethers. On the basis of high-resolution mass spectroscopy analysis, annulation presumably proceeded via a copper(I) difluorocarbene complex, which represents an unprecedented example of [4 + 1] cycloadditions promoted by a transition metal difluorocarbene complex.