Cathodic Radical Cyclisation of Aryl Halides Using a Strongly-Reducing Catalytic Mediator in Flow.

Area of Science:

• Organic Chemistry
• Electrochemistry
• Flow Chemistry

Background:

• Radical cyclization is a key synthetic strategy.
• Traditional methods often require harsh conditions or stoichiometric reagents.
• Electrochemistry offers a greener alternative for radical generation.

Purpose of the Study:

• To develop an efficient electro-reductive radical cyclization of aryl halides.
• To utilize an organic mediator for enhanced reactivity and selectivity.
• To apply the method in an undivided flow reactor for practical synthesis.

Main Methods:

• Employing an undivided flow reactor with steel and carbon electrodes.
• Utilizing a sub-stoichiometric amount of an organic mediator for electron transfer.
• Investigating the reaction mechanism, including homogeneous electron transfer.

Main Results:

• Successful synthesis of various hetero- and carbo-cycles, including tricyclic fused and spiro systems.
• Demonstrated the utility of sub-stoichiometric mediator (0.05 equiv).
• Showed that without mediator, hydrogenolysis of the C-X bond is the dominant pathway.

Conclusions:

• The developed electro-reductive radical cyclization is a practical and efficient method.
• The use of an organic mediator promotes the desired radical pathway over hydrogenolysis.
• This flow chemistry approach offers a sustainable alternative for synthesizing complex cyclic structures.