Synthesis, characterization and applications of densely functionalized pyridazines and fulvene-type compounds containing azulene moiety

Ethyl 4-ethoxyazulene-1-carboxylate (1) is highly efficient and novel substrate for electrophilic substitution reactions. These derivatives (2–4) were treated with NH2NH2/PhNHNH2 in ethanol to produce pyridazine, and fulvene derivatives with azulene frameworks (5, 6, 17, 19) via intramolecular cyclization. The substrates 5–8, 11, and 19 were effectively converted into densely functionalized heterocyclic molecules via Vilsmeier–Haack, Friedel–Crafts, and Michael addition reactions.