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Sterically Congested Protecting Group for a Boronyl Group in Iterative Aminations
Takaki Nojiri1, Naoki Tsuchiya1, Takashi Nishikata1
1Graduate School of Science and Engineering, Yamaguchi University, 2-16-1 Tokiwadai, Ube, Yamaguchi, 755-8611, Japan.
A novel α-hydroxycarboxamide protecting group stabilizes boron reagents for controlled amination reactions. This method enables precise synthesis of multi-arylamino substituted arenes via Chan-Evans-Lam or Buchwald-Hartwig amination.
Area of Science:
- Organic Chemistry
- Synthetic Methodology
- Boron Chemistry
Background:
- Boron reagents are versatile in organic synthesis.
- Protecting group strategies are crucial for controlling reactivity.
- Amination reactions are key for constructing C-N bonds.
Purpose of the Study:
- To develop a robust protecting group for boron reagents.
- To enable controlled amination of arylboron compounds.
- To achieve precise synthesis of poly-arylamino arenes.
Main Methods:
- Condensation of α-hydroxycarboxamide with arylboronic acid to form aryloxazaborolidinone (ArOxB).
- Utilizing Chan-Evans-Lam (C-E-L) or Buchwald-Hartwig (B-H) amination conditions.
- Employing Cu(II) catalysis for direct C-E-L amination in oxidative atmospheres.
Main Results:
- The α-hydroxycarboxamide moiety effectively protects the boronyl group.
- Reactivity of the C-B bond in ArOxB is tunable via steric and electronic effects.
- Successful amination reactions (C-E-L and B-H) were achieved while preserving the C-B bond.
- Direct C-E-L amination of ArOxB was demonstrated using Cu(II) activation.
Conclusions:
- The developed aryloxazaborolidinone (ArOxB) framework offers controlled reactivity for boron reagents.
- This methodology provides a precise route for synthesizing complex arylamino substituted arenes.
- The protecting group strategy is compatible with established amination protocols and offers new activation pathways.
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