Unveiling the Different Reactivity of Bent and Linear Three-Atom-Components Participating in [3 + 2] Cycloaddition Reactions

Abstract

The reactivity of a series of pairs of bent and linear three-atom-component (B-TACs and L-TACs) participating in [3 + 2] cycloaddition (32CA) reactions towards ethylene and electrophilic dicyanoethylene (DCE) have been studied within the Molecular Electron Density Theory. While the pseudodiradical structure of B-TACs changes to that of pseudoradical or carbenoid L-TACs upon dehydrogenation, zwitterionic B-TACs remain unchanged. Conceptual Density Functional Theory (CDFT) indices characterize five of the nine TACs as strong nucleophiles participating in polar reactions towards electrophilic ethylenes. The activation energies of the 32CA reactions with electrophilic DCE range from 0.5 to 22.0 kcal·mol−1, being between 4.3 and 9.1 kcal·mol−1 lower than those with ethylene. In general, B-TACs are more reactive than their L-TAC counterparts. A change in the regioselectivity is found in these polar 32CA reactions; in general, while B-TACs are meta regioselective, L-TACs are ortho regioselective. The geometrical parameters of the transition state structures suggest that the formation of the single bond involving the most electrophilic carbon of DCE is more advanced. A change in the asynchronicity in the reactions involving B-TACs and L-TACs is also found.

Keywords

• [3 + 2] cycloaddition reactions
• bent and linear three-atom-components
• reactivity
• regioselectivity
• molecular electron density theory