Mechanism Switch Between Radical-Polar Crossover and Radical Buffering

Area of Science:

• Organometallic Chemistry
• Catalysis
• Reaction Mechanisms

Background:

• Radical-polar crossover (RPC) is a key concept in one- and two-electron chemistry, particularly in Cr-catalyzed carbonyl additions.
• Understanding the mechanism of Cr-catalyzed carbonyl alkylation is crucial for developing new synthetic methodologies.

Purpose of the Study:

• To propose and validate a novel radical buffering scenario as an alternative bonding model for Cr-catalyzed carbonyl alkylation.
• To elucidate the factors influencing the mechanism switch between radical and polar pathways.
• To establish a new model for stereoselectivity control in asymmetric radical addition reactions.

Main Methods:

• Computational studies and experimental investigations were employed to verify the proposed radical mechanism.
• Analysis of factors such as radical stability, nucleophilicity, size, and the presence of heteroatoms or pi-bonds.
• Development of a stereoselectivity control model based on ligand-radical interactions.

Main Results:

• A radical buffering scenario was proposed and validated for Cr-catalyzed carbonyl alkylation.
• The mechanism switch between radical and polar models is influenced by specific radical properties and substrate features.
• A distinct stereoselectivity control model, differing from RPC, was demonstrated for the radical buffering scenario.

Conclusions:

• The radical buffering scenario provides a reliable mechanistic explanation for Cr-catalyzed carbonyl alkylation.
• This new model offers a different approach to stereoselectivity control in asymmetric radical addition reactions.
• A general model for enantioselectivity and diastereoselectivity in CrCl2/bisoxazoline-catalyzed reactions was established.