Synthesis, properties and molecular structure of a novel dicyanoheptafulvene derivative, 4′-dicyanomethylidenedispiro[cyclohexane-1, 1′-(1′,4′,7′-trihydrocyclopenta[f]azulene)-7′,1″-cyclohexane]

A novel dicyanoheptafulvene annulated by two spiro[4,5]deca-1,3-dienes was synthesized by the reaction of dispirocyclopentaazulenium cation with bromomalononitrile. Although was found to have a nonplanar heptafulvene structure by its X-ray crystallographic analysis, it is still capable of π-conjugation and thus shows appreciable contribution of the dipolar resonance form based on its spectroscopic data. The degree of the contribution was further evaluated for various dicyanoheptafulvenes in terms of the partial sum of atomic charges of the dicyanomethylene group in the calculated structures besides the interplanar angles of the heptafulvene part and the length of the exocyclic double bond in the crystal structures.