Visible-light-driven aromatization hydrogen evolution by organic dye and Ni complex

Abstract

Pyridine derivatives play an important role in curing and controlling mites, bacteria, weed and so on. Pyrimidine derivatives exist in a number of bioactive natural products, and they have anti-allergy, anti-cancer, anti-inflammatory, insecticidal and some other properties. 3,4-Disubstituted thiophenes not only are important units for the synthesis of natural products, but also serve as key components in some biologically active compounds and material chemistry. In modern society, we have the urgent demand for achieving our products atom economicly and environment-friendly. Under this background, "atom- economy" reactions have been drawing great attention from many chemists and they have got many exciting improvements since then. So, we want to make our own contributions to this area and the following are some of our preliminary results. Our method was based on synergistic application of eosin Y with nickel (II) complex and an external oxidant-free oxidative dehydrogenation aromatization has been developed. At room temperature, Hantzsch 1,4-dihydropyridines, 1,4-dihydropyrimidines, 2,5-dihydrothiophenes and 2,5-dihydropyrroles were transformed into corresponding aromatic compounds in excellent yield under visible light irradiation via hydrogen evolution. We determined the hydrogen with GC-TCD using pure hydrogen as an external standard. It features very mild reaction conditions, high yields and excellent chemo-selectivity. In the previous reports, these transformations usually required higher temperatures and/or stronger oxidizing reagents, resulting in the generation of a large amount of by-products. In addition, the hydrogen evolution reactions were also compared with those of aerobic dehydrogenation. The results indicated that the dehydrogenation aromatizations of hantzsch 1,4-dihydropyridines and 1,4-dihydropyrimidine derivatives under the hydrogen evolution conditions proceeded in higher yields but very low conversions, while the reactions of 2,5-dihydrothiophenes and 2,5-dihydropyrroles gave higher conversions in the aerobic dehydrogenation conditions. So far, this is the first report using organic dye material combined with nickel (II) complexes to achieve dihydrogen dehydrogenation aromatization of heterocyclic compounds.