In fact, since Hoffmann put forward the idea of C 18 in 1966 , several strategies have been proposed to try to achieve this unique allotropic carbon, including synthesis by eliminating the heteroatomic substituents of its various cyclocarbon precursors through methods such as retro-Diels-Alder reaction , decomplexation , decarbonylation , and [2+2] cycloreversion . One of the two recent pioneering experiments to prepare C 18 was achieved by sequentially removing a pair of carbonyl groups [(-CO) 2 ] from a cyclocarbon oxide C 18 -(CO) 6 , producing the C 18 -(CO) and C 18 -(CO) 2 molecules in turn, up to the final product C 18 . Actually as early as 30 years ago, Diederich and co-workers have successfully prepared C 18 -(CO) 6 molecule and determined it by X-ray diffraction with the same purpose . However, although cyclocarbon oxides are very special compounds with rich-carbon features, maybe blinded by the pursuit of pure all-carboatomic rings, they have not received the attention they deserve. And yet we believe that, at least till now, studying the easily synthesized and relatively stable cyclocarbon oxides C 18 -(CO) n (n = 6, 4, and 2) should have more practical significance than investigating the very reactive and hardly attainable C 18 .