Methyl 11-hydroxy-8-oxopentacyclo-[5.4.0.0(2,6).0(3,10).0(5, 9]undecanecarboxylate (3), C13H14-O4, M(r) = 234.26, triclinic, P1BAR, a = 7.291 (1), b = 7.441 (1), c = 10.414 (1) angstrom, alpha = 104.56 (1), beta = 90.41 (1), gamma = 99.07 (1)-degrees, V = 539.3 (1) angstrom 3, Z = 2, D(x) = 1.442 g cm-3, lambda-(Mo K-alpha) = 0.71073 angstrom, mu = 1.00 cm-1, F(000) = 248, T = 295 K, R = 0.0487 for 2138 reflections. Compound (3) contains four five-membered rings and a four-membered ring fused to form an open-ended cage structure. The through-bond interaction of the pi-systems in the parent diketone is absent in compound (3), which is reflected in the reduction of bond lengths. Although one C-C bond is 1.579 (2) angstrom, it has been shortened significantly. A hydrogen bond is formed between the hydroxyl group and the carbonyl O atom of the ester.