Synthesis of quinoxaline derivatives from terminal alkynes and o-phenylenediamines by using copper alumina catalyst

Abstract

Abstract: An efficient method for the synthesis of quinoxaline derivatives through oxidative coupling of o-phenylenediamines (OPD) with terminal alkynes by using copper-alumina (Cu-Al) catalyst was described. A series of Cu-Al catalysts with different mole ratios of Cu 2 +/ Al 3 +, 2:1 (Cu-Al-1), 2.5:1 (Cu-Al-2) and 3:1 (Cu-Al-3) were prepared by co-precipitation method followed by calcination and their activity was checked for the synthesis of quinoxaline derivatives. Cu-Al-2 showed excellent activity at 60∘C in presence of K 2CO 3. The catalyst is inexpensive, recyclable and environmentally benign. The fresh and recycled catalysts were characterized by different analytical techniques. Different reaction parameters were optimized; catalyst screening, solvent, base and temperature. The protocol was extended towards different substrates. Graphical Abstract: Synopsis. An efficient, robust and recyclable catalyst (Cu-Al catalyst) was developed for the synthesis of quinoxaline. A series of Cu-Al with different molar ratios of Cu 2 +/ Al 3 +, 2:1 (Cu-Al-1), 2.5:1 (Cu-Al-2) and 3:1 (Cu-Al-3) were prepared by co-precipitation method, followed by calcination and the activity of these catalysts was checked for the quinoxaline synthesis. Cu-Al-2 (2.5:1) was found to be the best catalyst with 95% yield of the desired product. [Figure not available: see fulltext.].