Choline chloride: 2 ZnCl2 catalyzed efficient one-pot regioselective synthesis of dihydrobenzofuro[2,3-b]benzofuran

The reaction of 2-naphthol and also para-substituted phenols with glyoxal in presence of choline chloride: 2 ZnCl2 [ChCl: 2ZnCl2], a deep eutectic solvent (DES), as a green catalyst was studied. The amount of catalyst, solvent type, temperature, and time on the yield of reaction were investigated. It was found that the optimal condition included 10% mol ratio of catalyst (mol percentage of DES to glyoxal), solvent-free condition (60 °C) and the time about one hour. Under these conditions, products are obtained in good yield (80%). The products were characterized on the basis of FT-IR, 1H-NMR, 13C-NMR spectra and comparison of melting point with authentic sample. The NMR spectra indicated that of the two probable isomers with an acetal and ether structure; the aforementioned reaction, regioselectively, furnished compounds with acetal linkage, rather than ether.