Theoretical study on mechanism of reaction between tert-butyl isocyanide and dimethyl acetylenedicarboxylate in presence of ethanethiol or thiophenol

The mechanism of the multicomponent reaction between tert-butyl isocyanide and dimethyl acetylenedicarboxylate in presence of ethanethiol and thiophenol (as SH-acid) was investigated theoretically. According to quantum-mechanical computations, four different pathways (I, II, III, and IV) were predicted for this reaction. The potential energy of all structures participating along the different reaction paths was evaluated. Also, the geometry of all structures (including reactants, transition states, intermediates, and products) was optimized in gas phase to determine the best reaction path and most stable products. To verify the effect of solvent on the potential energy surfaces, dichloromethane and acetone were subjected to condensed-phase calculations using the polarizable continuum model. The theoretical results suggested a reasonable mechanism for each path, indicating that the first step of each pathway was rate determining. Finally, natural bond orbital analysis was applied for further understanding of the molecular interactions.