N,O- and N,S-ketene acetals as substrates for aza-Claisen rearrangement

N,O-ketene acetals and N,S-ketene with a benzoyl group on the nitrogen are more stable than ketene acetals with a benzyl group on the nitrogen. These compds. undergo an aza-Claisen rearrangement. Due to high temps. and long reaction times needed, yields from N,O-ketene acetals are poor. N,S-ketene acetals are more stable than N,O-acetals, and temp. requirements to effect rearrangement are even higher. Catalysis, though attempted, could not be achieved. [on SciFinder(R)]