On the non-classical course of Polonowski reactions of N-benzylmorpholine-N-oxide (NBnMO)

The Polonowski reaction of NBnMO () afforded tropone () and the novel isoindole besides the expected products benzaldehyde and acetmorpholide, in a temperature-dependent ratio. The reaction proceeded via two primary carbenium–iminium ion intermediates, an exo-centered species which underwent a benzylium–tropylium type rearrangement, and a ring-centered species , which reacted further to isoindole by intramolecular electrophilic substitution. The experimental findings were in good agreement with DFT computational data.