Cycloadditionen von 6H‐1,3,4‐Oxadiazin‐6‐onen (4,5‐Diazaα‐pyronen), 11. δ‐Chlor‐δ‐lactone aus γ‐Oxoketenen

Cycloadditions of 6H-1,3,4-Oxadiazin-6-ones (4,5-Diaza-α-pyrones), 11. – δ-Chloro δ-Lactones from γ-Oxo Ketenes Prepared from 1,3,4-oxadiazinone 1 with norbornene, cyclopentene, cyclopentadiene, and indene, the γ-oxo ketenes 2, 5, 6, and 7 have been converted into the δ-chloro δ-lactones 3, 8, 9, and 10, respectively, by treatment with hydrogen chloride. The configuration of 10 has been determined by an X-ray structural analysis. These pseudo chlorides prove to be stable against methanol. Only in the presence of sulfuric acid as catalyst 3 suffers methanolysis to yield diester 4. On thermolysis, the γ-oxo ketenes are transformed into β-lactones. In particular, 6 and 7 gave 13 and 12, respectively. Formed also on photolysis of 6, β-lactone 13 partly isomerized to β-lactone 14 on prolonged heating.