Ru‐Catalyzed Sequential Dehydrogenative Friedlander Reaction/sp3 C–H Activation/Knovenagel Condensation in the Regioselective Synthesis of Chimanine B Analogues

Abstract

Choline chloride (ChCl) based deep eutectic solvent (DES), facilitated the regioselective synthesis of (E)‐1‐(4‐phenyl‐2‐styrylquinolin‐3‐yl)ethan‐1‐one (4), and (E)‐3‐phenyl‐1‐(4‐phenyl‐2‐((E)‐styryl)quinolin‐3‐yl)prop‐2‐en‐1‐ones, (5) from the corresponding 2‐amino‐5‐chloro benzhydrol, (1) in one‐pot strategy. The 2‐methyl‐3‐acetylquinoline generated in situ from the 2‐amino‐5‐chloro benzhydrol, (1) and acetyl acetone, (2) via dehydrogenative Friedlander reaction in DES could enable subsequent regio‐selective C‐2 methyl group sp3 C–H activation and rapid alkenylation with alcohols, (3) to provide the desired (E)‐2‐styrylquinolin‐3‐yl)ethan‐1‐ones, 4 in short reaction time and high yields and purity. Likewise, through the simultaneous C‐2 and C‐3 sp3 C–H activation with aromatic alcohols, (3) the (E)‐2‐styrylquinolin‐3‐yl)prop‐2‐en‐1‐ones, (5) formation was carried out in DES in high yields and purity. The physicochemical properties viz., UV/Vis, and fluorescence studies of the synthesized compounds were investigated. The absorption and emission properties of these luminophores are attributable to the presence of auxochromes in the 6‐position of quinoline moiety, styryl‐functional group at the 2‐position, and the enone group at 3‐position.