Procedure:  100 mL 1-neck flask, stirbar, septum, N₂ inlet

                  Added 4.020 g of oxime I to 30 g of PPA preheated to 120 C.  The mixture was stirred for 20 min at 120 C and poured hot into ~400 mL of ice water.  The mixture was stirred to rt and the resulting solid was collected by filtration.  The solid was then dissolved in ether, dried over MgSO₄, filtered and concentrated to ~50 mL by rotary evaporation.  A white solid formed.  Hexanes was added and the solid was collected by filtration.  The material was sufficiently pure for further elaboration at this point.  The product was a white, granular solid. 

 

¹H NMR (CDCl₃, 300 MHz) d 8.99 (s, NH, 1H), 7.24-7.01 (m, ArH, 4H), 2.78 (t, J = 6.9 Hz, CH₂, 2H), 2.35 (t, J = 7.1 Hz, CH₂, 2H). 

 

notes

 

In this rearrangement, protonation of the oxime is followed by migration of the aryl-oxime bond to form a carbocation intermediate.  Addition of water and regeneration of H⁺ followed by tautomerization gives the lactam. 

 

In the example shown, the aryl-oxime bond migrates preferentially to the alkyl-oxime bond to give a singular product.  However, in the case of alkyl-alkyl oximes, mixtures can be obtained.