Copper-Free Alternatives to Access Ketone Building Blocks from Grignard Reagents

Area of Science:

• Organic Chemistry
• Synthetic Chemistry
• Process Chemistry

Background:

• Grignard reactions are fundamental for carbon-carbon bond formation in industrial synthesis.
• Acid chlorides are traditionally used as electrophiles, often requiring additives like CuCl for optimal results.
• Developing more efficient and sustainable synthetic routes is crucial for large-scale chemical production.

Purpose of the Study:

• To evaluate acetic anhydride as a more effective electrophile than acetic chloride in Grignard reactions.
• To synthesize 4-fluoro-2-(trifluoromethyl)acetophenone, a key intermediate for agricultural active ingredients.
• To develop an additive-free Grignard reaction process suitable for large-scale manufacturing.

Main Methods:

• Investigated the reaction of Grignard reagents with acetic anhydride as an alternative electrophile.
• Compared the yield and selectivity against reactions using acetic chloride.
• Conducted computational mechanistic studies to understand the reaction behavior.

Main Results:

• Acetic anhydride matched and exceeded acetic chloride in terms of yield and selectivity.
• The reaction proceeded efficiently without the need for additives, simplifying the process.
• Acetic anhydride demonstrated greater tolerance to higher reaction temperatures compared to acetic chloride.

Conclusions:

• Acetic anhydride is a highly effective and advantageous electrophile for synthesizing ketones via Grignard reactions.
• The developed additive-free process offers significant benefits for industrial-scale production of key intermediates.
• Superior complexation of carboxylic acid anhydrides in the transition state likely explains the enhanced reactivity.