Stepwise Functionalization of a Pillar[5]arene-Containing [2]Rotaxane with Pentafluorophenyl Ester Stoppers

Area of Science:

• Supramolecular Chemistry
• Organic Synthesis

Background:

• Pillar[5]arenes are macrocyclic hosts with unique binding properties.
• Rotaxanes are mechanically interlocked molecules with potential applications in nanotechnology.
• Controlled functionalization of rotaxane building blocks is crucial for developing advanced materials.

Purpose of the Study:

• To investigate the stepwise bis-functionalization of pillar[5]arene-containing rotaxane building blocks.
• To explore the role of the pillar[5]arene moiety in directing functionalization and enabling the synthesis of dissymmetrical rotaxanes.
• To analyze the conformational behavior of these rotaxanes in different solvent environments.

Main Methods:

• Stepwise acylation reactions to introduce different stoppers.
• Nucleophilic substitution reactions for functionalization.
• Conformational analysis using spectroscopic techniques and computational methods.

Main Results:

• Selective mono-functionalization of the rotaxane was achieved due to the preferential positioning of the pillar[5]arene near the initial stopper.
• Dissymmetrical rotaxanes with distinct amide stoppers were successfully synthesized.
• The pillar[5]arene moiety effectively protected the axle during secondary functionalization, facilitating the synthesis of complex structures.
• Conformational analysis revealed that solvent polarity dictates the influence of polar versus solvophobic interactions on pillar[5]arene positioning.

Conclusions:

• Stepwise functionalization of pillar[5]arene rotaxanes offers a controlled route to dissymmetrical molecular architectures.
• The pillar[5]arene moiety serves as a dynamic protecting group, enabling challenging synthetic transformations.
• Solvent-mediated interactions significantly influence the conformational preferences of pillar[5]arene-based rotaxanes.