Derivatives of Ketipic Acid, II. – Ketipic Acid Dilactone and Related CompoundsThe highly reactive title compound 7 was prepared by thermal decomposition of the disguised oxalylbisketene 6. Ring opening of 7 with nucleophiles leads to γ‐alkylidenetetronic acids 4. α‐Substituted derivatives of 4a give rise to unsymmetrical dilactones 9a–c and the dibromodilactone 9d. The alkylidenetetronic acids are stabilized in the E configuration by hydrogen bridges. The pairs of isomeric (E)‐ and (Z)‐alkylidenetetronic acids 3 and 4 show characteristic spectral differences.