Diastereoselective Synthesis of α‑Fluoro-γ-lactams via Difluorocarbene-Triggered Cyclization and Rearrangement

Area of Science:

• Organic Chemistry
• Medicinal Chemistry
• Fluorine Chemistry

Background:

• Alpha-fluoro-gamma-lactams are important structural motifs in medicinal chemistry.
• Existing synthetic routes often rely on expensive fluorinating reagents.

Purpose of the Study:

• To develop a novel, cost-effective, and diastereoselective synthesis of alpha-fluoro-gamma-lactams.
• To explore the utility of difluorocarbene as a versatile building block for fluorine incorporation.

Main Methods:

• Utilized difluorocarbene generated from ethyl bromodifluoroacetate (EBDFA).
• Employed a base-mediated reaction with beta-aminoketones.
• Investigated reaction mechanisms using Density Functional Theory (DFT) calculations.

Main Results:

• Achieved a diastereoselective synthesis of alpha-fluoro-gamma-lactams.
• Demonstrated the cost-effectiveness by avoiding expensive fluorinating agents.
• Identified cyclization as the stereodetermining step, governed by Curtin-Hammett kinetics.
• Elucidated a reaction pathway involving a hemiaminal epoxide intermediate and nucleophilic fluoride ring-opening.

Conclusions:

• Developed a direct and modular synthetic route to stereodefined alpha-fluoro-gamma-lactams.
• Established difluorocarbene as a valuable C1 and F source for organic synthesis.
• Advanced the mechanistic understanding of difluorocarbene-mediated amine-carbonyl coupling reactions.