Umpolung of donor–acceptor cyclopropanes via N-heterocyclic carbene organic catalysis

A carbene-catalyzed formal umpolung of donor-acceptor (D-A) cyclopropanes is disclosed. The cyclopropane moiety is connected to an acetyl aldehyde that can be activated by a carbene catalyst. The initially electrophilic carbon attached to the donor group of the D-A cyclopropane aldehyde is inverted to form a nucleophilic reaction center. A subsequent reaction with isatins via a formal [3 + 2] process forms lactones bearing multiple functional groups with excellent enantio- and diastereoselectivities.