The deep eutectic melt of sorbitol and metformin hydrochloride: synthesis of 3-substituted 2-aminonaphtho[2,3-b]furan-4,9-diones and their photophysical properties

efficient and environmentally benign one-pot method is presented for the diverse synthesis of 3-substituted 2-aminonaphtho[2,3-b]furan-4,9-diones via the domino reaction between 2-hydroxy-1,4-naphthoquinone, beta-nitrostyrenes and ammonium acetate in a new deep eutectic solvent made of sorbitol and metformin HCl. A pronounced positive solvatochromism was observed for the electrondonor-acceptor conjugated system of these products, resulting in bathochromic and hyperchromic shifts of their visible absorption band in polar and protic solvents. A red-shift of about 30 nm was observed on going from non-polar to polar solvents and gave rise to a distinct colour change.