The Reaction of Diphenylcyclopropenone with 1-Azirines. Synthetic and Mechanistic Implications

1-Azirines 1 react with, diphenylcyclopropenone (2) to produce 1:1 adducts, which were proven to be 2,3-di-pheny1-4-pyridones 6. That the 3 substituents in 6 originate from the 3 substituents on the azirine was shown by independent synthesis of 6a as well as by isolation of the 3f-4-pyridone 10 when 2-pheny1-3,3-dimethylazirine was used as a substrate. These results suggest a nucleophilic attack by the azirine nitrogen on C-2 of the cyclopropenone with subsequent rupture of the azirine 3-1 bond (C-N). The mechanistic pathway of the reaction is discussed.