Electrochemical Allene C─H Functionalization via Carbanion Sampling.

Area of Science:

• Organic Chemistry
• Catalysis
• Synthetic Methodology

Background:

• C─H bond functionalization is key for upgrading simple molecules.
• Reaction selectivity is typically dictated by C─H bond acidity and bond dissociation energy (BDE).
• Overcoming these constraints is crucial for functionalizing challenging molecules.

Purpose of the Study:

• To develop a novel strategy for unconventional selectivity in allene C(sp2)─H functionalization.
• To enable the synthesis of thermodynamically unfavored products.
• To expand the scope of C─H functionalization for complex organic synthesis.

Main Methods:

• A chromium-catalyzed hydrogen evolution reaction.
• An electrochemical protocol for in situ generation of allene carbanions.
• A dynamic carbanion sampling strategy.
• Density functional theory (DFT) calculations and control experiments.

Main Results:

• Achieved abnormal site-selective functionalization of 1,3-disubstituted allenes at less acidic C(sp2)─H sites.
• Observed isomerization and functionalization of 1,1-substituted allenes to alkynes.
• Synthesized unprecedented allene products with high versatility for late-stage derivatization.
• Demonstrated convergent synthesis of functionalized allenes from alkynes or mixed substrates.

Conclusions:

• The carbanion sampling strategy effectively breaks traditional selectivity constraints in allene functionalization.
• The developed method provides access to novel, synthetically valuable organic compounds.
• The findings open new avenues for challenging C─H functionalization reactions.