Reaction of Benzazulene with Dimethyl Acetylenedicarboxylate. Formation of a ?-Bond Fixed Heptalene Derivative

Article abstract of DOI:10.1016/0040-4039(94)02176-C

Reaction of benzazulene with dimethyl acetylenedicarboxylate (DMAD) in tetralin at 200 deg C gave a new ?-electron system, dimethyl benzoheptalene-6,7-dicarboxylate and dimethyl indeno<1,2,3-cd>azulene-5,6-dicarboxylate.The reaction of a non-fused azulene, 6-isopropyl-1-phenylazulene, gave extremely different results indicating strong effects of the fused benzene ring on the reactivities of azulenes with DMAD.Coupling constants of the protons on the seven-membered ring and variable temperature 1H NMR of the heptalene indicated ?-bond fixation of the molecule.