An efficient pathway to high persistence length helicenes from scalable [4]-helicene synthons

Area of Science:

• Organic Synthesis
• Materials Science
• Chiroptical Materials

Background:

• Helicenes are polycyclic aromatic hydrocarbons with a unique helical structure.
• Developing efficient synthetic routes to high-persistence length helicenes is crucial for advanced applications.
• Controlling stereochemistry and enhancing yields in helicene synthesis remain significant challenges.

Purpose of the Study:

• To report a convergent synthetic strategy for high-persistence length helicenes.
• To demonstrate the utility of a novel menthyloxycarbonato-[4]-helicene synthon.
• To enable the development of chiroptical responsive strain sensors.

Main Methods:

• Convergent synthesis utilizing a regioselective menthyloxycarbonato-[4]-helicene synthon.
• Palladium-mediated cross-couplings (Stille and Heck) for precursor synthesis.
• Mallory-type photo-induced annulation with controlled temperature and subsequent recrystallization for diastereo-enrichment.

Main Results:

• A menthyloxycarbonato-[4]-helicene synthon was accessed in 84% yield.
• Bis(menthyloxycarbonato)-[11]-helicene diastereomers were successfully prepared.
• Photoreaction temperature control (>40 °C) enhanced [11]-helicene yields from 7% to 42% by minimizing byproduct formation.
• Recrystallization achieved diastereo-enrichment of the final products.

Conclusions:

• The reported synthetic strategy provides efficient access to high-persistence length helicenes.
• The developed [4]-helicene building block is versatile for constructing complex helical structures.
• This work lays the foundation for embedding enantiopure helicenes into polymers for chiroptical responsive strain sensors.