A high-yielding, ligand-free, palladium-catalyzed isocyanide insertion reaction for the synthesis of phthalazino[1,2-b]quinazolinones from the readily obtainable quinazolinones has been developed. Easily handled and relatively low-cost palladium(II) acetate was used as the catalyst, without an additional ligand. Preparation of the quinazolinones involved the cascade reaction of isatoic anhydrides, phenylhydrazines and 2-bromobenzaldehyde catalyzed by p-toluenesulfonic acid in one pot. This novel protocol may be applicable for the synthesis of other important ring-fused heterocyclic compounds.
Key words
ligand-free - palladium catalysis - isocyanide insertion reaction - ring-fused quinazolinones - depropargylation
