A Computational Evaluation of the Evidence for the Synthesis of 1,3‐Dimethylcyclobutadiene in the Solid State and Aqueous Solution

Density functional calculations of ¹H NMR spectra and reaction barriers at the ωB97XD/6‐311G(d,p)/continuum water level do not support the claimed identification of encarcerated 1,3‐dimethylcyclobutadiene in either the solid state or aqueous solution, as reported by Barboiu et al (Chem. Eur. 2011 , 17, 10021). Instead, previous suggestions that the species identified in the solid state is in fact 2‐oxabicyclo2.2.0]hex‐5‐en‐3‐one (the Dewar lactone Me₂2 ) are reaffirmed. Analysis of the ground‐state electronic structure of this species indicates an unusual π‐anomeric effect is promoting a Dunitz‐like chemical reaction pathway leading to the eventual elimination of carbon dioxide and formation of 1,3‐dimethylcyclobutadiene.