Rapid Access to Amino-Substituted Quinoline, (Di)Benzofuran, and Carbazole Heterocycles through an Aminobenzannulation Reaction

The use of a powerful aminobenzannulation reaction has been applied for the synthesis of amino-substituted quinolines, dibenzofurans, and carbazoles. The precursors are heterocycles bearing a methyl ketone group ortho to an internal alkyne. They are commercially available or can be obtained in three to four classical and efficient reactions: Vilsmeier−Haack, Sonogashira (diversity point), Grignard, and Ley’s oxidation. Upon aminobenzannulation reaction—classical conditions being pyrrolidine neat or in a solvent and 4 Å MS—an interesting range of disubstituted quinolines, dibenzofurans, and carbazoles are obtained along with enamine formation in some cases. The reaction is useful since meta-substituted heterocycles are produced and also differs from classical heterocyclic methods which go through closure at the heteroatom-containing ring instead of benzene ring formation.