One-pot synthesis and AFM imaging of a triangular aramide macrocycle

Area of Science:

• Organic Chemistry
• Supramolecular Chemistry
• Materials Science

Background:

• Macrocyclization reactions are fundamental in synthesizing complex organic molecules.
• Cyclic aramides offer unique structural and material properties.
• Controlling polymerization versus macrocyclization is a key challenge.

Purpose of the Study:

• To investigate the macrocyclization of N-benzylated phenyl p-aminobenzoates.
• To understand the role of protecting groups in directing cyclic versus linear product formation.
• To characterize the self-assembly of the synthesized cyclic aramides.

Main Methods:

• Self-condensation reactions using lithium bis(trimethylsilyl)amide (LiHMDS).
• Density Functional Theory (DFT) calculations to model reaction pathways.
• High-resolution Atomic Force Microscopy (AFM) for surface imaging.

Main Results:

• Efficient synthesis of three-membered cyclic aramides (molecular triangles) with high yields.
• Demonstrated necessity of an ortho-alkyloxy substituent on the N-benzyl group for macrocyclization.
• Observed exclusive formation of linear polymers in the absence of the ortho-alkyloxy group.
• AFM imaging revealed self-assembly of molecular triangles in groups of four on a calcite surface due to templating and hydrogen bonding.

Conclusions:

• The ortho-alkyloxybenzyl protecting group is essential for directing the self-condensation towards macrocyclization.
• DFT modeling provides insights into the selectivity of the reaction.
• The synthesized molecular triangles exhibit ordered self-assembly on surfaces, influenced by intermolecular forces and surface interactions.