A novel type of donor-acceptor cyclopropane with fluorine as the donor: (3+2)-cycloadditions with carbonyls

gem-Difluorocyclopropane diester is disclosed as a new type of donor-acceptor cyclopropane, which smoothly participates in (3 + 2)-cycloadditions with various aldehydes and ketones. This work represents the first application of gem-difluorine substituents as an unconventional donor group for activating cyclopropane substrates in catalytic cycloaddition reactions. With this method, a wide variety of densely functionalized gem-difluorotetrahydrofuran skeletons, which are otherwise difficult to prepare, could be readily assembled in high yields under mild reaction conditions. Computational studies show that the cleavage of the C-C bond between the difluorine and diester moieties occurs upon a S(N)2-type attack of the carbonyl oxygen.