A Molecular Electron Density Theory Study of the Polar Diels-Alder Reaction of Naphtoquinone:Cr(CO)3 Complex with Cyclic Dienes

The role of the Cr(CO)(3) coordination to the aromatic ring of naphtoquinone (NQ) in the polar Diels-Alder (P-DA) reactions with cyclic dienes, cyclopentadiene (Cp), cyclohexadiene (Ch), and 1-methoxy-cyclohexadiene (ChOMe), has been studied within Molecular Electron Density Theory (MEDT). Electron Localization Function (ELF) of the NQ:Cr(CO)(3) complex indicates that Cr(CO)(3) does not cause any remarkable change in the electronic structure of NQ. While the NQ:Cr(CO)(3) complex is categorized as a strong electrophile, the cyclic dienes are categorized as strong nucleophiles, suggesting P-DA reactions. Formation of the NQ:Cr(CO)(3) complex reduces the activation energy by only 0.7 kcal center dot mol(-1). While Ch shows a lower reactivity than Cp, ChOMe presents the highest reactivity of this series of cyclic dienes. Analysis of the activation Gibbs free energies of the P-DA reaction with Cp indicates that the reaction is completely endo and anti stereoselective. The present MEDT study shows that the Cr(CO)(3) complex has no effective catalytic activity in the P-DA reactions of NQ with cyclic dienes, but only permits the reaction to take place experimentally with a total endo and anti facial stereoselectivity, yielding a single cycloadduct.

Automated summary

The role of Cr(CO)(3) coordination in the polar Diels-Alder reactions of naphtoquinone has been studied using Molecular Electron Density Theory. It was found that Cr(CO)(3) does not significantly affect the electronic structure of naphtoquinone. While the formation of the NQ:Cr(CO)(3) complex reduces the activation energy by a small amount, the complex does not exhibit effective catalytic activity in the reactions with cyclic dienes.