The chemistry of 6-dialkylamino-2H-1,3-oxazin-2-ones. Reversible thermal ring-opening and cycloaddition reactions with N-arylmaleimides and 1-diethylaminopropyne. X-Ray crystal structures of a 5H-2-pyridone and a 1H-2-pyridone

Abstract

Flash-vacuum pyrolysis of the 1,3-oxazin-2-ones (1) and (9) gave the valence-isomeric carbamoylvinyl isocyanates (8) and (10), respectively, which recyclised to the oxazinones at room temperature. The oxazinones reacted with N-arylmaleimides in a Diels–Alder fashion; with 1-diethylaminopropyne, however, the first oxazinone yielded the isomeric pyridones (17) and (21), whose structures were determined by X-ray analysis.