Catalytic Boration of Alkyl Halides with Borane without Hydrodehalogenation Enabled by Titanium Catalyst

Area of Science:

• Organometallic Chemistry
• Catalysis
• Organic Synthesis

Background:

• Transition-metal catalysis is crucial for C-B bond formation.
• Alkyl halide boration often suffers from side reactions like hydrodehalogenation.
• Developing selective and general methods for alkyl boronate ester synthesis remains a challenge.

Purpose of the Study:

• To report a novel titanium-catalyzed boration of alkyl (pseudo)halides.
• To demonstrate the suppression of hydrodehalogenation using titanium catalysts.
• To synthesize a diverse range of alkyl boronate esters.

Main Methods:

• Titanium-catalyzed reaction of alkyl halides (iodides, bromides, chlorides, mesylates) with boranes (HBpin, HBcat).
• Screening of titanium catalysts and reaction conditions.
• Mechanistic studies to elucidate the reaction pathway.

Main Results:

• Achieved unprecedented and general titanium-catalyzed boration of various alkyl electrophiles.
• Successfully suppressed hydrodehalogenation, a common issue with other transition metals.
• Synthesized diverse alkyl boronate esters from primary, secondary, and tertiary alkyl halides, including unactivated alkyl chlorides.
• Demonstrated functional group tolerance (ester, alkene, carbamate).
• Preliminary mechanistic studies suggest a radical pathway.
• Extended the methodology to aryl bromides.

Conclusions:

• Titanium catalysis offers a superior approach for alkyl halide boration, minimizing side reactions.
• The developed method provides a versatile route to synthetically useful alkyl boronate esters.
• The reaction's broad scope and functional group tolerance make it highly applicable in organic synthesis.