Imidoylketene - oxoketenimine rearrangement. Facile 1,3-shift of an alkoxy group

Thermal CO extrusion from 2,3-dihydropyrrole-2,3-dione 3 generates imidoylketene 4, which cyclizes to 2-methoxy-4-quinolone (6). Using flash vacuum pyrolysis and low temperature IR spectroscopy, it is shown that 4 interconverts with ketenimine 5 prior to cyclization to 6.