1,4-Diazabicyclo[2.2.2]octane-Mediated Ring Opening of 1-Acetylcyclopropanecarboxamides and Its Application to the Construction of 3-Alkylated γ-Lactams

1,4-Diazabicyclo[2.2.2]octane (DABCO)-mediated ring opening of 1-acetylcyclopropanecarboxamides efficiently gave stable zwitterions that could be formed in situ or readily isolated. An application of this novel type of ring opening was demonstrated in a one-pot efficient construction of biologically interesting 3-alkyl γ-lactams. The Lewis-base protocol provides an opportunity for performing ring opening, cycloaddition, and rearrangement reactions of donor–acceptor cyclopropanes through organocatalysis.