Selectivity emerges from indiscriminate photoreduction

Area of Science:

• Organic Chemistry
• Photoredox Catalysis
• Reaction Mechanisms

Background:

• Single electron transfer (SET) is a fundamental organic reaction mechanism.
• Controlling SET selectivity based on substrate redox potentials is challenging, especially for difficult-to-reduce substrates.
• Existing methods limit coupling reactions involving thermodynamically challenging substrates.

Purpose of the Study:

• To introduce a novel selectivity paradigm for outer sphere SET reactions.
• To demonstrate that substrate redox potentials can be rendered irrelevant in SET reactions.
• To enable selective radical annulation reactions involving thermodynamically mismatched substrates.

Main Methods:

• Utilizing super-potent photoreductants to achieve diffusion-limited SET.
• Leveraging competition between downstream chemical steps and back electron transfer (BET) for selectivity control.
• Applying the principles to radical annulation reactions between cyclopropyl ketones and alkenes.

Main Results:

• Demonstrated that substrate redox potentials do not dictate SET selectivity when using super-potent photoreductants.
• Achieved selective radical annulation between cyclopropyl ketones and alkenes, overcoming a volt of unfavorable reduction potential.
• Established a new selectivity profile governed by kinetic factors beyond redox potential.

Conclusions:

• Developed a general blueprint for designing SET reactions that bypass traditional redox potential control.
• Opened new avenues for coupling reactions involving challenging substrates.
• Highlighted the potential of photoredox catalysis in redefining reaction selectivity.