Harnessing Ionic Interactions and Hydrogen Bonding for Nucleophilic Fluorination

Area of Science:

• Organic Chemistry
• Reaction Mechanisms
• Fluorination Chemistry

Background:

• Nucleophilic fluorination is crucial for synthesizing fluorinated organic compounds.
• Ionic liquids and hydrogen bonding are increasingly recognized as influential factors in reaction outcomes.
• Understanding these non-covalent interactions is essential for developing efficient synthetic methodologies.

Purpose of the Study:

• To review recent advancements in nucleophilic fluorination.
• To elucidate the roles of Coulombic interactions and hydrogen bonding in these reactions.
• To highlight strategies for optimizing fluorination reactions through tailored promoters and solvent engineering.

Main Methods:

• Review of literature on nucleophilic fluorination, including S_N2 and S_NAr pathways.
• Analysis of mechanistic features involving ionic liquids, alkali metal fluorides, and diaryliodonium salts.
• Examination of the impact of ionic liquid components, hydrogen bonding, and protecting group positioning on reaction efficiency.

Main Results:

• Ionic liquids can act as bifunctional activators in S_N2 fluorination.
• Coulombic interactions and hydrogen bonding significantly affect the efficiency of S_NAr fluorination, particularly with guanidine-containing diaryliodonium salts.
• The position of protecting groups, like Boc, influences fluorination yields due to proximity effects on nucleophile location.
• Recent progress in synthesizing [¹⁸F]F-dopa via S_NAr fluorination is discussed.

Conclusions:

• Tailor-making promoters and solvent engineering based on ionic interactions and hydrogen bonding are effective strategies for optimizing nucleophilic fluorination.
• A deeper understanding of non-covalent interactions allows for precise control over reaction outcomes.
• These insights are applicable to both general organic synthesis and the development of radiopharmaceuticals.