Using Calcium Carbide as an Acetylene Source for Cascade Synthesis of Pyrrolo[2,3‐b]quinoxalines via Copper‐Free Sonogashira Coupling Reaction

A palladium‐catalyzed cascade protocol has been established for the synthesis of 4‐methyl‐1‐(1H‐pyrrolo2,3‐b]‐quinoxalin‐2‐yl)cyclohexanols and 2‐phenyl‐1‐(1H‐pyrrolo2,3‐b]quinoxalin‐2‐yl)propan‐1‐ols through the reaction of N‐alkyl(aryl)‐3‐chloroquinoxalin‐2‐amines with calcium carbide and cyclohexanones or 2‐phenylpropanal. This one‐pot process, carried out without any copper salt in the key step of the Sonogashira coupling reaction, provides an efficient method for the synthesis of 2,3‐disubstituted pyrrolo2,3‐b]quinoxalines in the presence of catalytic amounts of Pd(PPh₃)₂Cl₂ in DMSO/H₂O with high yields. The benefit of this strategy is the use of a commercially available, inexpensive, and less hazardous primary chemical feedstock, calcium carbide, as an acetylene source in a wet solvent.