The carbenoid-type reactivity of simplest nitrile imine from a molecular electron density theory perspective

Abstract

The [3 + 2] cycloaddition (32CA) reactions of the simplest nitrile imine with ethylene and electrophilic dicyanoethylene have been studied within the Molecular Electron Density Theory (MEDT) with the aim of characterising its reactivity. Topological analysis of the electron localisation function of NI shows that it has a carbenoid structure. The activation energy of the 32CA reaction of the simplest nitrile imine with dicyanoethylene is 5.6 kcal mol−1 lower than that involving ethylene, in agreement with the high polar character of the former reaction. Bonding Evolution Theory accounts for the cb-type reactivity of nitrile imine. Along the more favourable ortho regioisomeric path associated with the 32CA reaction involving dicyanoethylene, which takes place through a non-concerted two-stage one-step mechanism, formation of the first C3-C4 single bond takes place at a C-C distance of 2.02 Å, by donating the non-bonding electron density of the carbenoid center of nitrile imine to the β-conjugated C4 carbon of dicyanoethylene.