Nucleophile-Assisted Alkene Activation: Olefins Alone Are Often Incompetent

Area of Science:

• Organic Chemistry
• Catalysis
• Reaction Mechanisms

Background:

• Organocatalytic enantioselective halocyclizations are crucial for forming new bonds under controlled conditions.
• Simple alkenes often react slowly with conventional halenium donors, necessitating mechanistic understanding.
• The AdE3 mechanism, involving concerted electrophilic addition with nucleophile participation, is key to stereocenter control.

Purpose of the Study:

• To explore how nucleophile proximity and basicity modulate alkene reactivity and halocyclization rates.
• To analyze factors influencing the spectrum of halocyclization reactivity, from stepwise to concerted.
• To provide insights for designing new organocatalytic alkene addition reactions.

Main Methods:

• Detailed spectroscopic analysis of starting materials.
• Assessment of addition stereopreferences.
• Isotope effect studies and nucleophile-alkene interaction analyses.

Main Results:

• Alkene reactivity spans from stepwise electrophilic attack to nucleophile-assisted alkene activation (NAAA).
• Nucleophile proximity and basicity significantly influence reaction rates and mechanisms.
• Demonstrated control over reactivity across the stepwise-to-concerted spectrum.

Conclusions:

• Understanding nucleophile influence is critical for controlling organocatalytic halocyclizations.
• Findings offer a framework for predicting and designing stereoselective and regioselective alkene additions.
• The study advances the mechanistic understanding of catalytic alkene functionalization.