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Sequential Pd-catalyzed asymmetric allene diboration/alpha-aminoallylation
Joshua D Sieber1, James P Morken
1Department of Chemistry, Venable and Kenan Laboratories, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3290, USA.
Journal of the American Chemical Society
|January 5, 2006
Summary
This study introduces a new palladium-catalyzed method for enantioselective diboration of allenes. This process yields valuable vinyl boronates for selective allylation reactions, leading to chiral Mannich products or homoallylic amines.
Area of Science:
- Organic Chemistry
- Catalysis
- Asymmetric Synthesis
Background:
- Allenes are versatile synthetic precursors.
- Enantioselective synthesis of boronates is crucial for complex molecule construction.
- Palladium catalysis offers efficient routes to valuable organic transformations.
Purpose of the Study:
- To develop a novel palladium-catalyzed enantioselective diboration of prochiral allenes.
- To explore the utility of the resulting vinyl boronates in subsequent selective reactions.
- To provide access to enantiomerically enriched Mannich products and homoallylic amines.
Main Methods:
- Palladium-catalyzed enantioselective diboration reaction using prochiral allenes.
- Allylation reactions of the generated vinyl boronates with primary imines.
- Oxidation of allylation products to yield Mannich products.
- Protonation and Suzuki cross-coupling of vinyl boronates for homoallylic amine synthesis.
Main Results:
- Successful enantioselective diboration of prochiral allenes.
- High selectivity in allylation reactions with primary imines.
- Access to nonracemic Mannich products with 87-97% enantiomeric excess (ee) via oxidation.
- Generation of enantiomerically enriched homoallylic amine derivatives through protonation and Suzuki coupling.
Conclusions:
- The developed Pd-catalyzed diboration is an effective method for synthesizing chiral vinyl boronates.
- These boronates serve as key intermediates for accessing valuable chiral amine derivatives.
- The methodology offers a versatile route to enantiomerically enriched Mannich products and homoallylic amines.