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

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

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