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.
Die Cycloadditionsprodukte der Titelverbindungen (IV) [Darstellung analog der Literatursynthese von (IVa) aus den entsprechenden (I) und (II)] mit Alkenen ergeben unter N2‐Verlust Keten‐Intermediate wie (VI) [aus dem trans‐Olefin (V)], deren Auftreten (außer bei TFA‐katalysierten Reaktionen) z.T. IR‐spektroskopisch bzw. durch Abfangreaktionen [vgl.
Aus dem Oxadia‐zi‐non (I) entsteht mit Norbornen (II) ein isolierbares, kristallines Primäraddukt (III), das in Lösung Stickstoff unter Bildung des γ‐Ketoketens (IV) abspaltet.
ChemInform Abstract Reaction of the readily prepared suspended oxadiazinone (II) with norbornene (IIIa) or norbornadiene (IIIb) gives rise to the Diels-Alder adducts (IV) which are stable only in the crystalline state. In solution, they are decomposed to give the oxoketenes (V) and β-lactones (VI). The compounds (V) can be prepared directly from solutions of (II) and (III). Cycloalkenes such as (VII) or (IX) are converted by (II) mainly into ketones such as (VIII) or (X). Evidence is given for the intermediacy of dihydropyryliumolates in the thermal denitrogenation of the Diels-Alder adducts of (II), e.g. (IVa), (IVb).
Das Oxadiazinon (Ia) reagiert nicht mit cis‐Cycloocten und cis‐1,5‐Cyclooctadien, mit dem trans‐1‐Cycloocten (II) erhält man jedoch über die spektrokopisch nachweisbare Zwischenstufe (III) ein Cyclisierungsprodukt (IV).
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