Synthesis, stability and molecular structure of novel hydrocarbon cations consisting of a tropylium cation and two spiro[4.5]deca-2,4-dienes

Two novel hydrocarbon cations with a tropylium ion ring fused by two spiro[4,5]deca-2,4-dienes, and , were synthesized by a six-step sequence starting from 1,6- and 1,5-diacetyl-1,3,5-cycloheptatrienes, respectively. The pKR+ values of and were found to be the same at 13.2, providing a new access to highly stable cations. The density functional calculations predict that both and have cyclohexane rings with the chair conformation spread toward molecular edges as the most stable structure. The crystal packing and structure of including dichloromethane were also elucidated by X-ray crystallographic analysis.