Sydnone-Based Approach to Heterohelicenes through 1,3-Dipolar-Cycloadditions

Area of Science:

• Organic Chemistry
• Synthetic Chemistry
• Supramolecular Chemistry

Background:

• Helicenes are polycyclic aromatic hydrocarbons with a unique helical structure.
• Pyrazole-containing compounds exhibit diverse applications in medicinal chemistry and materials science.
• Developing efficient synthetic routes to complex molecular architectures like helicenes remains a key challenge.

Purpose of the Study:

• To establish the first synthetic strategy for pyrazole-containing helicenes.
• To investigate the regioselectivity of the sydnone-aryne [3 + 2]-cycloaddition reaction in this context.
• To elucidate the factors governing the observed regioselectivity using computational methods.

Main Methods:

• Utilizing sydnone-aryne [3 + 2]-cycloaddition for helicene synthesis.
• Employing extended aromatic scaffolds to influence reaction outcomes.
• Performing Density Functional Theory (DFT) calculations to analyze reaction mechanisms and selectivity.

Main Results:

• Successful synthesis of pyrazole-containing helicenes.
• Observation of unprecedented regioselectivity, favoring sterically constrained isomers.
• Identification of electronic and steric factors driving the regioselectivity through DFT analysis.

Conclusions:

• The sydnone-aryne [3 + 2]-cycloaddition provides a viable route to pyrazole-containing helicenes.
• Extended aromatic systems can direct cycloaddition regioselectivity towards sterically demanding products.
• DFT calculations are crucial for understanding complex selectivities in organic reactions.