O-ylide and π-complex formation in reactions of a carbene with dibenzo and monobenzo crown ethers.

Reactions of p-nitrophenylchlorocarbene (PNPCC) with various dibenzo crown ethers produce O-ylides and π-complexes; the reactions can be followed via the spectral signatures of the carbene and the products. The O-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 O-ylides; monobenzo π-complexes are either not formed in significant concentrations or are spectroscopically silent.