Two-Way Catalysis in a Diels-Alder Reaction Limits Inhibition Induced by an External Electric Field

Area of Science:

• Computational chemistry
• Physical organic chemistry
• Chemical catalysis

Background:

• Oriented external electric fields (EEFs) are known to influence chemical reactivity and selectivity.
• The Diels-Alder (DA) reaction is a fundamental transformation in organic chemistry sensitive to electronic perturbations.

Purpose of the Study:

• To investigate the catalytic and selective effects of EEFs on Diels-Alder reactions, specifically BDE-DA and CPDE-DA.
• To introduce and define the electrostatic resistance point (ERP) as a metric for EEF-induced reaction control.
• To explore the relationship between substituent effects, stereoselectivity, and EEF response.

Main Methods:

• Density functional theory (DFT) calculations, specifically using the B3LYP functional.
• Analysis of reaction pathways and transition states under varying EEF strengths.
• Quantification of the electrostatic resistance point (ERP) and its relation to stereoselectivity (ΔERP).

Main Results:

• EEFs can switch from inhibiting to enhancing reaction rates, with a defined electrostatic resistance point (ERP) marking this transition.
• Both normal and inverse electron-demand DA reactions exhibit catalytic activity influenced by EEF direction and ERP.
• C5 substituents on cyclopentadiene modulate ERP values, indicating their role in resisting EEF effects.
• Distinct ERP values for endo and exo transition states correlate with stereoselectivity (ΔERP).

Conclusions:

• EEFs offer a tunable method to control Diels-Alder reaction selectivity and rate.
• The ERP serves as a valuable quantitative measure for predicting and understanding EEF-driven chemical transformations.
• Stereoselectivity in DA reactions can be modulated and understood through the lens of electrostatic interactions and ERP values.