The formation of azulene derivatives from 2H-cyclohepta[b]furan-2-one derivatives

3-Ethoxycarbonyl- and 3-acetyl-2H-cyclohepta[b]furan-2-ones react easily with malonitrile. cyanoacetamide, ethyl cyanoacetate and diethyl malonate, in the presence of sodium ethoxide or t-butyl-amine, giving the corresponding 1,2,3-trisubstituted azulene derivatives, respectively. The structures of these azulene derivatives are determined on the basis of chemical evidence, and spectral data. Considering the structural correlation between the starting 2H-cyclohepta[b]furan-2-ones and the azulene derivatives obtained, a reasonable reaction course, involving the heptafulvene-type and dihydroazulene-type intermediates, is presented for the formation of azulene derivatives from 2H-cyclohepta[b]furan-2-ones.