Efficient synthesis and applications of 2-substituted azulene derivatives: towards highly functionalized carbo- and heterocyclic molecules

An efficient synthesis of 2-substituted azulene derivatives (3–6) was accomplished from ethyl 2-oxo-2H-cyclohepta[b]furan-3-carboxylate 1 and its derivative 2, which in turn were prepared from readily available tropolone. Compounds 1 and 2 were utilized to construct densely functionalized benz[a]azulene and azulene-furan frameworks (16–25, 29–34, 37, 38).