Prediction on the origin of chemoselectivity in Lewis base-mediated competition cyclizations between allenoates and chalcones: a computational study
The origin of chemoselectivities of Lewis base (LB) organocatalyst mediated competing [3 + 2] and [4 + 2] cyclizations of allenoates and chalcones has been predicted by performing DFT calculations. These kinds of reactions start from the complexation of different LBs with allenoates to form the zwitterionic intermediate, which reacts with chalcones via different [α,β]-[4 + 2], [β,γ]-[4 + 2], and [α,γ]-[3 + 2] cyclization pathways. In order to explore the general principle of these kinds of LB-mediated cyclizations, we have suggested a new route for predicting the origin of chemoselectivities by comparing the energy difference of the HOMOTS and p-orbital coefficient/contribution of center atoms in the HOMOTS of the key transition states. In addition, local reactivity index analyses (such as nucleophilic and electrophilic Parr functions) were also used for providing valuable insights for predicting the possible active sites of the allenoate. This work would be useful for rational design of the LB-mediated multiple cyclization reactions of allenoates in the future.