Synthesis, molecular structure, and chemical reactivity of azuleno[1,2-a]acenaphthylene

The azuleno[1,2-a]acenaphthylene () was prepared from 1-pyrrolidinylacenaphthylene () and 2H-cyclohepta[b]furan-2-one () by the method of the Takase–Yasunami azulene synthesis. Its 1H and 13C NMR spectra indicate that comprises azulene and naphthalene rather than acenaphtylene and heptafulvene in accordance with speculation drawn from a previous study of the DEPE calculations. The solid-state structure of was elucidated by X-ray crystallographical analysis, indicating that is nearly planar and exhibits little bond alternation as seen in the optimized structure at the MB3LYP/6-311G∗ level of theory. All bond lengths observed by the X-ray analysis are in good agreement within 0.024 Å with those calculated. Under pyrolytic conditions underwent azulene–naphthalene rearrangement to give and . The electrophilic substitution of was observed at the 7-position and the second reaction at the 3-position. The cycloaddition reaction of with dimethyl acetylenedicarboxylate (DMAD) yielded the 1:1 cycloadduct with a heptalene skeleton and the 1:2 cycloadduct , along with the substitution product . The X-ray structural analysis of the cycloadducts and is also described.