S. Kuroda et al., SYNTHESIS AND PROPERTIES OF AZULENO[1,2-A]ACENAPHTHYLENE AND DIMETHYLACENAPHTHYLENO[1,2-D]HEPTALENE-8,9-DICARBOXYLATE, Chemistry Letters, (1), 1994, pp. 85-88
The parent compound of azuleno[1,2-a]acenaphthylene (8) was synthesize
d, and its H-1 NMR spectrum suggests no bond alternation in the azulen
e moiety. The cycloaddition of 8 with dimethyl acetylenedicarboxylate
gave an acenaphthyleno[1,2-d]heptalene derivative.