1993 ring closure reactions ring closure reactions O 0130
-103Cycloadditions of 6H-1,3,4-Oxadiazin-6-ones (4,5-Diaza-α-pyrones) . Part 12. Dieckmann Condensations without Bases.-Addition of the diazapyrone (I) to norbornene, norbornadiene or styrene gives rise to oxoketenes such as (III) and (VIII) which on treatment with MeOH are converted into semiacetals like (V) and (IX) and the expected diesters. Formation of semiacetals proceeds via a related Dieckmann condensation mechanism including intramolecular (1,2) migration of a methoxy group. -(CHRISTL, M.; LANZENDOERFER, U.; GROETSCH, M. M.; HEGMANN, J.; DITTERICH, E.; HUETTNER, G.; PETERS, E.-M.; PETERS, K.; VON SCHNERING, H. G.; Chem.