A DFT study on the mechanisms of three-component reaction between imidazoles, isocyanates and cyanophenylacetylene

In this paper, two possible competitive reaction channels, including the C(2)-vinylation of 1-substituted imidazoles with cyanophenylacetylene (channel 1) and the three-component reaction to form N-(Z)-alkenylimidazole-2-carbomide with the presence of isocyanates (channel 2), have been investigated in detail using density functional theory (DFT). There are three reaction processes in channel 1: the formation of zwitterion, proton transfer, and ring rearrangement. The channel 2 share the same processes in the former two steps (i.e. formation of zwitterion and the proton transfer), then the intermediate carbene reacts with another reactant isocyanate, and the last step is also a ring rearrangement process. Our calculated results indicate that channel 2 is more energy favorable than channel 1, so the product of the channel 2 is the main product, which is in good agreement with the experimental results. Moreover, our calculated results show that the solvent effects have little influence on the selectivity in this reaction. The detailed reaction mechanisms should be helpful for people to understand the three-component reaction at molecular level, and the suggested novel bimolecular proton transfer process provides some valuable insights on rational design of the efficient Brّnsted acid/base catalysts for this type of reaction.