A radical [3 + 2]-cycloaddition reaction for the synthesis of difluorocyclopentanones

Herein we disclose a novel radical-mediated [3 + 2]-cycloaddition reaction of alkenes under photochemical conditions. A set of rationally designed bromodifluoromethyl alkynyl ketones were prepared and applied in the cascade reaction. The protocol features broad functional group tolerance and excellent regio- and stereo-selectivity. Both activated and unactivated alkenes were suitable substrates. The transformation gives rise to a variety of valuable alpha,alpha-difluorocyclopentanones bearing a tetra-substituted E-alkene.