The simple compound apparently has yet to be observed (as of 2009). In 1998, however, P. Strazzolini and others have claimed the synthesis of dioxane tetraketone (C4O6), which can be viewed as the cyclic dimer of oxalic anhydride.
^Paolo Strazzolini, Alberto Gambi, Angelo G. Giumanini and Hrvoj Vancik (1998). "The reaction between ethanedioyl (oxalyl) dihalides and Ag2C2O4: a route to Staudinger’s elusive ethanedioic (oxalic) acid anhydride". J. Chem. Soc., Perkin Trans. 1 (16): 2553–2558. doi:10.1039/a803430c.
^Ahmed A. El-Sherif, Bakir J. A. Jeragh (2007), Mixed ligand complexes of Cu(II)-2-(2-pyridyl)-benzimidazole and aliphatic or aromatic dicarboxylic acids: Synthesis, characterization and biological activity. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, volume 68, issue 1, pages 877-882. doi:10.1016/j.saa.2006.12.073
^M. M. Rauhut, L. J. Bollyky, R. A. Clarke, M. Loy, B. G.Roberts (1965) CHEMILUMINESCENT MATERIALS. Technical Report 9 (AD0621845), Defense Technical Information Center, 78 pages.