Direct deoxygenative borylation of carboxylic acids

Area of Science:

• Organic Chemistry
• Organoboron Chemistry
• Synthetic Methodology

Background:

• Carboxylic acids are versatile building blocks, but their conversion to boronic acids via deoxygenation is underexplored.
• Existing methods like decarboxylative borylation are well-established, yet alternative pathways are needed.
• The inertness of carboxylic C-O bonds presents a significant synthetic challenge.

Purpose of the Study:

• To develop a novel deoxygenative borylation reaction for synthesizing boronic acids from carboxylic acids.
• To explore the transformation of both aromatic and aliphatic carboxylic acids.
• To establish a metal-free synthetic route for accessing alkylboronates and trisboronates.

Main Methods:

• Utilizing bis(catecholato)diboron (B2cat2) as a Lewis acidic and reducing reagent.
• Performing deoxygenative borylation of free carboxylic acids and their sodium salts.
• Investigating the reaction with aromatic and aliphatic carboxylic acids under metal-free conditions.

Main Results:

• Successfully synthesized a range of benzylboronates from aromatic carboxylic acids.
• Developed a facile triboration process for aliphatic carboxylic acids, yielding 1,1,2-alkyl(trisboronates).
• Demonstrated a stepwise C-O bond cleavage mechanism, providing mechanistic insights.

Conclusions:

• Established an efficient, metal-free deoxygenative borylation of carboxylic acids.
• Expanded the synthetic accessibility of valuable organoboron compounds, including alkylboronates and trisboronates.
• The mechanistic understanding may guide future reductive functionalization of oxygenated feedstocks.