The synthesis and characterization of a series of new olefin-substituted closo-1,12-[C2B10H12] compounds is described. The reaction of deprotonated closo-1,12-dicarbadodecaborane with 7-methoxycycloheptatriene yields the cycloheptalriene-substituted carborane compound, closo-[1-(1-C7H7)-12-(H)-C2B10H10] (3). Deprotonation of 3 with butyllithium and subsequent reaction with 3,4-dimethyl-2-cyclopenten-1-one was found to yield the bis-olefin-substituted carbinol compound [1-(1-C7H7)-12-(C5H4-1-(OH)-3,4-(CH3)(2))-C2B10H10] (5) in good yield. Acidic dehydration of 5 quantitatively converted it into the simple bis-olefin cage compound [1-(1-C7H7)-12-(C5H3-3,4(CH3)(2))-C2B10H10] (6). Finally, thermal treatment of 6 in refluxing toluene was employed to prepare the isomerized cycloheptatriene compound [1-(4-C7H7)-12-(C5H3-3,4-(CH3)(2))-C2B10H10] (7) in high yield. These compounds represent the first metal-free cyclopentadiene and bis-olefin large cluster species reported in which the Cs ring is attached directly to the cage. The complete characterization of products by multinuclear NMR (H-1, B-11, and C-13), infrared, UV-visible, and mass spectroscopic analyses is presented. The X-ray crystal structures of 3 and 7 are also reported. X-ray data for 3: triclinic system, space group P (1) over bar with cell constants a = 6.6807(3) Angstrom, b = 10.2939(3) Angstrom, c = 10.3962(4) Angstrom, alpha = 89.342(2)degrees, beta = 74.610(2)degrees gamma = 83.373(2)degrees, Z = 2, R1 = 0.0487 (wR2 (all data) = 0.1272). X-ray data for 7: monoclinic system, space group P2(1)/c with cell constants a = 7.7207(7) Angstrom, b = 15.8730(14) Angstrom, c = 15.5493(13) Angstrom, beta = 99.146(2)degrees, Z = 4, R1 = 0.0761 (wR2 (all data) = 0.2050).