Copper-catalyzed Synthesis Of Quinoxalines With O-phenylenediamine And Terminal Alkyne In The Presence Of Bases

A novel way of synthesizing quinoxalines efficiently through cyclization of o-phenylenediamine and terminal alkyne by Cu(Ⅱ) and bases is developed. This reaction undergoes smoothly to give the products in moderate to good yields. Quinoxalines play an important role in the area of nitrogen-containing heterocycles as they are useful intermediates of other organic cyclic compounds and are useful dyes. And its derivatives possess significant biological activities including antiviral, antibacterial and anti-inflammatory. In addition, the quinoxalines are well known in the pharmacological industry.During the last decades, many methods have been developed for the preparation of quinoxalines. Most of them utilized o-phenylenediamine and alkyne which is oxidized to diketone. Numerous oxidants and catalytic systems for this process have been reported:DMSO/PdX2, PdCl2/CuCl2/PEG, KMnO4/NaHCO3, SO3/dioxane, I2/DMSO, O2/Cu, Ga(OTf)3. Although they are efficient methods for quinoxalines, most of them make use of elevated temperature, prolonged reaction time, toxic oxidants and functionalized substrates. Here we developed a novel method to synthesize quinoxalines with o-phenylenediamine and phenylacetylene catalyzed by Cu(OAc)2·H2O in the presence of bases.