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

Abstract

The azuleno[1,2- a]acenaphthylene ( 1a ) was prepared from 1-pyrrolidinylacenaphthylene ( 5 ) and 2 H-cyclohepta[ b]furan-2-one ( 6 ) by the method of the Takase–Yasunami azulene synthesis. Its 1H and 13C NMR spectra indicate that 1a 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 1a was elucidated by X-ray crystallographical analysis, indicating that 1a 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 1a underwent azulene–naphthalene rearrangement to give 9 and 10 . The electrophilic substitution of 1a was observed at the 7-position and the second reaction at the 3-position. The cycloaddition reaction of 1a with dimethyl acetylenedicarboxylate (DMAD) yielded the 1:1 cycloadduct with a heptalene skeleton 16a and the 1:2 cycloadduct 19 , along with the substitution product 17 . The X-ray structural analysis of the cycloadducts 16a and 19 is also described.