<i>O</i>‑Ylide and π‑Complex Formation in Reactions of a Carbene with Dibenzo and Monobenzo Crown Ethers

Reactions of <i>p</i>-nitrophenylchlorocarbene (PNPCC) with various dibenzo crown ethers produce <i>O</i>-ylides and π-complexes; the reactions can be followed via the spectral signatures of the carbene and the products. The <i>O</i>-ylides form most rapidly, but over time they decay in favor of the more stable π-complexes. Extensive computational studies support and refine appropriate structural and mechanistic conjectures. Reactions of PNPCC with monobenzo crown ethers afford only the spectral signatures of <i>O</i>-ylides; monobenzo π-complexes are either not formed in significant concentrations or are spectroscopically silent.