Converting Strain Release into Aromaticity Loss for Activation of Donor–Acceptor Cyclopropanes: Generation of Quinone Methide Traps for C‑Nucleophiles

Here, we present a new approach for the activation of
donor–acceptor
cyclopropanes in ring-opening reactions, which does not require the
use of a Lewis or Brønsted acid as a catalyst. Donor–acceptor
cyclopropanes containing a phenolic group as the donor undergo deprotonation
and isomerization to form the corresponding quinone methides. This
innovative strategy was applied to achieve (4 + 1)-annulation of cyclopropanes
with sulfur ylides, affording functionalized dihydrobenzofurans. Additionally,
the generated ortho- and para-(aza)quinone
methides can be trapped by various CH-acids.