Electrophilic activation of CO2 in cycloaddition reactions towards a nucleophilic carbenoid intermediate: new defying insights from the Molecular Electron Density Theory

Abstract

The electrophilic activation of the two C=O double bonds of CO2 in the cycloaddition reactions involved in the domino reaction between methyl isocyanide, acetylenedicarboxylate and CO2 yielding a spiro-compound has been studied within the Molecular Electron Density Theory (MEDT) at the MPWB1K/6-311G(d,p) computational level. The approaching mode of the carbonyl groups of CO2 and lactone to the high nucleophilic carbenoid intermediate generated in the first reaction of this domino process promotes the C–C bond formation and the subsequent ring closure. MEDT analysis of cycloaddition reactions involved in this domino process enables to understand the molecular mechanism of these [2n + 2n] cycloadditions, which is different from the previously proposed [4π + 2π] cycloadditions derived from the Frontier Molecular Orbital theory.