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.