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

Abstract

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·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.

Keywords:

• Diels-Alder reactions
• Cr(CO)₃ complex
• molecular electron density theory
• reactivity
• naphtoquinone
• cyclic dienes

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work has been supported by the Ministry of Science and Innovation (MICINN) of the Spanish Government, project PID2019-110776GB-I00 (AEI/FEDER, UE). This work has also received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 846181 (MRG).