Novel ring transformation of mesoionic oxazoles into 2(1H)-pyrazinones by the reaction with TosMIC

Abstract Treatment of mesoionic 1,3-oxazolium-5-olates with TosMIC in the presence of a base causes a novel ring transformation affording 2(1 H )-pyrazinones in moderate yields. The origin of C-2 carbonyl oxygen in the product was elucidated to be molecular oxygen, based on 18 O-labeling experiments.