Jf. Stambach et al., REARRANGEMENT OF 1-OXA-5-AZABICYCLO[5.5]UNDEC-2-EN-4-ONES TO 5,6,7,8-TETRAHYDROQUINOLIN-2(1H)-ONES, Synthesis, (3), 1998, pp. 265-266
Spiro compounds 1 are easily converted into tetrahydroquinolin-2-ones
2 in a one step reaction involving anhydrous strong acidic conditions.
A plausible mechanism is discussed.