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

Mar Ríos-Gutiérrez,Fatemeh Ghodsi,Luis Domingo

doi:10.3390/org2030014

Mar Ríos-Gutiérrez, Fatemeh Ghodsi + Show 1 more

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https://doi.org/10.3390/org2030014

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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.

Highlights

2] cycloaddition (32CA) reactions, which involve the 1,3-addition of an ethylene to a three[3 + 2] cycloaddition (32CA) reactions, which involve the 1,3-addition of an ethylene to a atom-component (TAC), are an important type of cycloaddition allowing three-atom-component (TAC), are an important type of cycloaddition allowthe formation of five-membered heterocycles of great pharmaceutical and industrial ining the formation of five-membered heterocycles of great pharmaceutical and industrial terest [2,3]
This Molecular Electron Density Theory [4] (MEDT) study is divided into three parts: (i) first, the electronic structures of BTACs and L-TACs based on electron localisation function [21] (ELF) analysis and Natural Population Analysis (NPA) are compared; (ii) the participation of B-TACs and L-TACs in polar 32CA reactions is analyzed within CDFT; and (iii) the 32CA reactions of the nine TACs 1–8 with ethylene 9 and DCE 10 are explored in order to compare the reactivity of B-TACs and L-TACs in non-polar and polar processes
The topological analysis of the ELF has proven to be a powerful tool to establish a straightforward connection between the electron density distribution and the chemical structure [21]

Summary

Introduction

Cycloaddition reactions are one of the most useful tools in organic synthesis as they Cycloaddition reactions are one of the most useful tools in organic synthesis as they permit to obtain cyclic compounds with a regio- and/or stereoselective fashion [1,2]. Permit to obtain cyclic compounds with a regio- and/or stereoselective fashion [1,2]. Atdistributed under the terms and tribution (CC license (http://creaconditions of BY)

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