Amine exchange in formamidines: an experimental and theoretical study

Area of Science:

• Organic Chemistry
• Supramolecular Chemistry

Background:

• N-H-containing formamidines exhibit strong association with carboxylic acids, forming complexes with defined geometries.
• Protonation enhances formamidine electrophilicity, facilitating amine exchange reactions.
• The prototropic equilibrium allows the formamidine core to act as a bisimine, enabling exchange of both amine fragments.

Purpose of the Study:

• To investigate the use of carboxylic acids as templates for synthesizing defined molecular architectures via dynamic amine exchange in formamidines.
• To elucidate the mechanisms and rules governing amine exchange in formamidine-carboxylic acid complexes.
• To demonstrate the feasibility of templated macrocycle formation through dynamic exchange.

Main Methods:

• Complexation of N-H-containing formamidines with carboxylic acids.
• Protonation studies to induce electrophilicity enhancement.
• Analysis of amine exchange reactions with various nucleophiles (aliphatic amines, aromatic amines, alkoxyamines).
• Characterization of reaction products and determination of exchange rules.

Main Results:

• Three distinct amine exchange regimes were identified based on the incoming amine nucleophile.
• Specific exchange rules were established concerning the nature of the amine leaving groups.
• A proof-of-concept demonstration of carboxylic acid-templated macrocycle synthesis was achieved.

Conclusions:

• Carboxylic acids effectively template dynamic amine exchange in formamidines.
• The understanding of exchange regimes and rules facilitates the rational design of molecular synthesis.
• This methodology offers a novel pathway for constructing complex macrocyclic structures.