Arene C-H borylation strategy enabled by a non-classical boron cluster-based electrophile

Area of Science:

• Synthetic Organic Chemistry
• Organoboron Chemistry
• Catalysis

Background:

• Direct C-H borylation of unactivated C-H bonds, especially in sterically hindered arenes, remains a significant challenge in synthetic chemistry.
• Existing methods often rely on transition metals or directing groups, limiting their applicability to complex substrates.

Purpose of the Study:

• To develop a novel, precious metal-free synthetic strategy for the C-H borylation of sterically hindered alkyl- and haloarenes.
• To enable the synthesis of aryl boronic esters that are difficult to access via current direct C-H borylation methods.

Main Methods:

• A two-step sequence involving electrophilic aromatic substitution (EAS) using a boron cluster electrophile (Cs2[closo-B10H10]) followed by cage deconstruction.
• The first step forms a B-C bond via cage-opening of the boron cluster.
• The second step utilizes diols to promote cage deconstruction and yield the aryl boronic ester.

Main Results:

• Successful synthesis of aryl boronic esters from sterically hindered arenes, which are typically challenging substrates.
• The reaction proceeds without the need for precious metals, specialized ligands, pre-functionalized boron reagents, or strictly inert conditions.
• The boron cluster electrophile intermediate (B10H13+) provides unique steric and electronic control over regioselectivity, avoiding side reactions.

Conclusions:

• A new, efficient, and versatile method for synthesizing aryl boronic esters from hindered arenes has been established.
• This precious metal-free approach expands the scope of C-H borylation, offering a valuable tool for organic synthesis.
• The unique reactivity of the boron cluster electrophile enables selective functionalization of challenging substrates.