A Practical, Ligand-Free, Palladium-Catalyzed Isocyanide Insertion Reaction for the Construction of Novel Ring-Fused Quinazolinones

Abstract

A high-yielding, ligand-free, palladium-catalyzed isocyanide insertion reaction for the synthesis of phthalazino[1,2-<i>b</i>]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 <i>p</i>-toluenesulfonic acid in one pot. This novel protocol may be applicable for the synthesis of other important ring-fused heterocyclic compounds.