Regiochemical Control in Triptycene Formation-An Exercise in Subtle Balancing Multiple Factors.

Area of Science:

• Organic Chemistry
• Supramolecular Chemistry
• Reaction Mechanism Studies

Background:

• Triptycenes are complex polycyclic aromatic hydrocarbons with unique three-dimensional structures.
• Controlling the stereochemistry of triptycene formation is crucial for designing novel molecular architectures.
• Anthracene derivatives serve as key precursors in synthesizing complex organic molecules.

Purpose of the Study:

• To investigate the influence of substituents at the 10-position of 1,8-dichloroanthracenes on the stereochemical outcome of reactions with ortho-chloroaryne.
• To understand the factors governing the formation of syn- and anti-trichlorotriptycene isomers.
• To explore the predictive power of computational methods in elucidating reaction pathways.

Main Methods:

• Synthesis of substituted 1,8-dichloroanthracenes.
• Reaction of substituted 1,8-dichloroanthracenes with ortho-chloroaryne.
• Analysis of reaction products using NMR spectroscopy, mass spectrometry, and X-ray diffraction.
• Quantum chemical calculations, including transition state analysis.

Main Results:

• Reactions yield mixtures of syn- and anti-trichlorotriptycenes, with isomer ratios dependent on the 10-substituent.
• Electropositive substituents (SiMe3, GeMe3) promote syn-isomer formation.
• Bulky tert-butyl groups (CMe3) exclusively yield the anti-isomer.
• Computational studies highlight the role of dispersion forces in predicting stereochemical outcomes, despite some conflicting results.

Conclusions:

• The nature of substituents on the anthracene precursor significantly directs the stereoselectivity of triptycene formation.
• Dispersion forces play a critical role in the regiochemical control of these reactions.
• Experimental characterization confirms the structures of syn-trichlorotriptycenes with electropositive substituents.