Choline chloride: 2 ZnCl_2 catalyzed efficient onepot regioselective synthesis of dihydrobenzofuro[2,3b]benzofuran

The reaction of 2naphthol and also parasubstituted phenols with glyoxal in presence of choline chloride: 2 ZnCl_2 [ChCl: 2ZnCl_2], 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), solventfree 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 FTIR, 1HNMR, 13CNMR 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.