The Reaction of Oxazoles with Singlet Oxygen. IV. Imino Anhydride Intermediates

Reaction o f 2-aryl-4,5-polymethylene oxazoles w i t h s i n g l e t oxygen y i e l d s N-aroyl imino anhydrides.I f the polymethylene bridge i s l a r g e enough a f u r t h e r rearrangement t o t r i a m i d r s may take place.Previous r e p o r t s on the reactions of s i n g l e t oxygen w i t h oxazoles have shown t h a t oxygen uptake leads t o triamides, most probably, through intermediate imino anhydride^."^'^While these imino anhydrides are too r e a c t i v e t o be i s o l a t e d i n the oxygenations of monocyclic oxazoles, they may be i s o l a t e d i n the case o f fused-ring systems.Thus, the s i n g l e t oxygen o x i d a t i o n of 2-phenylcyclohexeno-4,