DFT study on reaction mechanisms of propylamine and dimethyl acetylenedicarboxylate with 1,3-dimethylalloxan

In an attempt to explore the mechanism for the multicomponent reaction of propylamine and dimethyl acetylenedicarboxylate with 1,3-dimethylalloxan, two reaction mechanisms were investigated using density function theory (DFT) at the B3LYP/6-311++G(d,p) level of theory, including the solvent effect of dichloromethane simulated by PCM. One is proton migration mechanism and the other is the new mechanism that avoids all the complicated proton transfer processes along a simple route. The new mechanism is the most energetically favorable pathway. Specifically, it contains two tandem processes: Firstly, the propylamine reacts with dimethyl acetylenedicarboxylate to form a zwitterionic intermediate. Secondly, it is a stepwise [2 + 3] cycloaddition of the zwitterionic intermediate with 1,3-dimethylalloxan to give the final product via elimination of a methanol molecule. The reaction can occur easily at room temperature, which is in good agreement with available experiment.