Controlling site selectivity in Pd-catalyzed oxidative cross-coupling reactions.
Thomas W Lyons1, Kami L Hull, Melanie S Sanford
1Department of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor, Michigan 48109, USA.
This study reveals how quinone promoters and carboxylate ligands control site selectivity in palladium-catalyzed oxidative coupling reactions. Ligand substitution can reverse selectivity, offering new synthetic control for arene functionalization.
Area of Science:
- Organic Chemistry
- Catalysis
- Synthetic Methodology
Background:
- Palladium-catalyzed oxidative coupling is crucial for C-H functionalization.
- Controlling site selectivity in these reactions remains a challenge, especially for complex arenes.
Purpose of the Study:
- To investigate factors governing site selectivity in Pd-mediated oxidative coupling of substituted arenes.
- To explore the impact of promoter and ligand properties on reaction outcomes.
- To understand the mechanistic basis for observed selectivity trends.
Main Methods:
- Systematic variation of quinone promoter concentration, steric, and electronic properties.
- Steric and electronic modulation of carboxylate ligands.
- Investigation of ligand substitution (carboxylate to carbonate).
- Analysis of reaction products to determine site selectivity.
Main Results:
- Quinone promoter properties significantly influence site selectivity.
- Steric and electronic features of the carboxylate ligand play a key role.
- Replacing carboxylate with carbonate ligands reverses site selectivity for many arene substrates.
- Observed trends are rationalized through mechanistic considerations.
Conclusions:
- Site selectivity in Pd-catalyzed oxidative coupling is tunable via promoter and ligand design.
- Understanding these factors enables predictable functionalization of arenes.
- This work provides valuable insights for developing new synthetic strategies in organic chemistry.
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