Highly Distorted Multiple Helicenes: Syntheses, Structural Analyses, and Properties

Area of Science:

• Organic Chemistry
• Supramolecular Chemistry
• Materials Science

Background:

• Helicenes are chiral aromatic hydrocarbons with unique helical structures.
• Developing new synthetic routes for complex helicene architectures is crucial for exploring their properties.

Purpose of the Study:

• To synthesize novel hexapole helicenes (HHs) and nonuple helicenes (NHs).
• To investigate their unique structural features and develop efficient synthetic methodologies.
• To explore their chiroptical properties and computational prediction of diastereomers.

Main Methods:

• Two-step synthesis involving iodocyclization and palladium-catalyzed annulation.
• X-ray crystallography for three-dimensional structure elucidation.
• Chiral resolution and experimental determination of enantiomerization barrier.
• Density functional theory (DFT) calculations for diastereomer energy prediction.

Main Results:

• Successful synthesis of HHs and NHs with a shared terminal naphthalene unit.
• Elucidation of crystal structures for three C1-symmetric HHs and one C3-symmetric NH.
• Experimental determination of the enantiomerization barrier for a HH (31.2 kcal/mol).
• Development of a DFT-based method for predicting diastereomer stability.

Conclusions:

• A facile and regioselective synthetic route for complex helicenes was established.
• The synthesized HHs and NHs exhibit unique structural motifs.
• Computational methods can efficiently predict diastereomer stability, aiding in the design of novel helicene architectures.