FVP of triazole 13 produces the isolableketenimine 11 together with indole 15.11 undergoesreversible interconversion with imidoylketene 10 above 380°C. The latter cyclizes to quinolone12. Meldrum's acid derivative 16 producesthe same ketene 10 above 200 °C, and thelatterisomerizes to ketenimine 11 at 200 °C by a 1,3-shift of aMeO group. A competing elimination ofMeOH from 16 produces (phenylimino)propadienone20.