Abstract:
A simple, metal-free protocol is reported for the one-pot synthesis of 2-styrylquinolines using a combination of 1,3-dimethyl urea (1,3-DMU) and L-tartaric acid (LTA) (in 3:1 ratio) as deep eutectic solvent (DES). The reaction proceeds via Friedlander annulation followed by Knoevenagel condensation (sp3 C-H activation) to give functionalized styrylquinoline derivatives with good to excellent yields. Density functional theory (DFT) calculations supported the experimental results and role of DES in the enolization of carbonyl compound (for Friedlander annulation) and formation of enamine, a key step in the sp3 C-H activation. Further, the absorbance, emission spectra of the resulting acyclic, cyclic compounds was recorded and found that the compound 7c showed highest emission band maxima (644 nm) due to the intramolecular charge transfer. Also compounds 7b, 8d exhibited larger bathochromic shift at 551nm, & 558 nm respectively and compound 5n showed highest Stokes shifts (?? -182 nm). Compound 7e displayed noticeable colors in various solvents (solvatochromic effects). Some of the resulting compounds reported here can be used for developing fluorescent probes.