Theoretical modeling of homogenous gold-catalyzed or NaH-supported alkyne cyclization

Abstract

Gold-catalyzed or NaH-supported formation mechanisms of pyrazine and diazepines were investigated computationally. The structural properties of these heterocyclic compounds were studied in the gas phase and various solvents. Density functional theory, including B3LYP, WB97X-D, M06-2X, and M06 hybrid functional methods, was used to locate and discuss the energetics of the intermediates and the transition states. The nature of the substituents attached to the terminal alkyne played an essential role in these mechanisms. Electron-donating or electron-withdrawing substituents indicated in which direction the cyclization would evolve. Natural bond orbital analysis was performed to determine the chemoselectivity of the products.