Photoexcited Intramolecular Annulative Cross-Coupling via an EDA Complex Mechanism.

Area of Science:

• Organic Chemistry
• Green Chemistry
• Photochemistry

Background:

• Transition-metal-free cross-coupling reactions are crucial for sustainable organic synthesis.
• Developing efficient metal-free strategies for constructing complex molecular architectures is an ongoing challenge.

Purpose of the Study:

• To report a metal- and additive-free strategy for intramolecular C-halogen/C-H cross-coupling.
• To construct phenanthrene cores using readily accessible diarylethenes.
• To elucidate the mechanistic pathway of this photoinduced reaction.

Main Methods:

• Utilizing E/Z-mixed diarylethenes as starting materials.
• Employing a strategy involving rapid E → Z isomerization.
• Initiating radical cyclization under mild, photoinduced conditions.

Main Results:

• Successful construction of phenanthrene cores via intramolecular C-halogen/C-H cross-coupling.
• Demonstration of a chain pathway involving photoisomerization and single-electron transfer (SET).
• Identification of electron donor-acceptor (EDA) complex-mediated SET as a key step.

Conclusions:

• This work provides a practical and sustainable route to phenanthrene derivatives.
• The study offers significant mechanistic insights into metal-free, photoinduced C(Ar)-halogen bond activation.
• The developed methodology highlights the potential of diarylethenes in green synthetic chemistry.