Ruthenium-Catalyzed Formation of Quinolines via Reductive Cyclization of Nitroarenes with Tris(3-hydroxypropyl)amine in an Aqueous Medium

Nitroarenes react with tris(3-hydroxypropyl)amine in an aqueous medium (dioxane/H₂O) at 180° in the presence of a catalytic amount of a ruthenium catalyst and tin(II) chloride along with isopropanol as hydrogen donor to afford the corresponding quinolines in good yields. The presence of tin(II) chloride is essential for the formation of quinolines. A reaction pathway involving initial reduction of nitroarenes to anilines, propanol group transfer from tris(3-hydroxypropyl)amine to anilines to form 3-anilino-l-propanols, N-alkylation of anilines by 3-anilino-1-propanol to form 1,3-dianilinopropane and intramolecular heteroannulation of 1, 3-dianilinopropane is proposed for this catalytic process.