1-Azadienes in heterocyclic synthesis. Reaction of 1-N-alkyl-1-azapenta-1,3-dienes with mesoionic oxazolones

1-N-Alkyl-1-azapenta-1,3-dienes 2 smoothly reacted with various mesoionic oxazolones 1 to afford 3,4-di-hydro-2-pyridones 3 in excellent yields and there was no evidence for the formation of any products arising from the cycloaddition on the carbon? carbon double bond or on the azomethine function.