Hydroquinone/Quinone Cycle for Reductive Photocatalytic Transformations

Area of Science:

• Organic Chemistry
• Photochemistry
• Catalysis

Background:

• Phenanthrenequinones can be converted to phenanthrenehydroquinones (H₂PQs) using visible light and alcohols.
• H₂PQs function as catalytic organic photoreductants.

Purpose of the Study:

• To investigate the efficacy of H₂PQs in deoxygenating N-heterocyclic N-oxides.
• To explore the mechanism of H₂PQs as photoreductants under visible light.

Main Methods:

• In situ generation of H₂PQs from phenanthrenequinones under visible light.
• Deoxygenation reactions with various N-heterocyclic N-oxides.
• Analysis of reduction potentials and mechanistic insights using TD-DFT calculations.

Main Results:

• H₂PQs efficiently deoxygenate diverse N-heterocyclic N-oxides.
• The photoreduction occurs even with substrates having more negative reduction potentials than H₂PQ.
• Evidence suggests hydrogen bonding assists electron transfer in the process.

Conclusions:

• H₂PQs are effective photoacids and photoreductants.
• The hydroquinone/quinone cycle can be harnessed for visible-light-driven reductions.
• This study introduces a novel catalytic system for organic photoreduction.