B(C sub(6)F sub(5)) sub(3)-Catalyzed Hydrogenation of Oxime Ethers without Cleavage of the N--O Bond

The hydrogenation of oximes and oxime ethers is usually hampered by N--O bond cleavage, hence affording amines rather than hydroxylamines. The boron Lewis acid B(C sub(6)F sub(5)) sub(3) is found to catalyze the chemoselective hydrogenation of oxime ethers at elevated or even room temperature under...

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Bibliographic Details
Published inAngewandte Chemie International Edition Vol. 53; no. 48; pp. 13278 - 13281
Main Authors Mohr, Jens, Oestreich, Martin
Format Journal Article
LanguageEnglish
Published 01.11.2014
Subjects
Bonding
Boron
Cleavage
Elevated
Ethers
Fracture mechanics
Hydrogenation
Lewis acid
Oximes
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Summary:The hydrogenation of oximes and oxime ethers is usually hampered by N--O bond cleavage, hence affording amines rather than hydroxylamines. The boron Lewis acid B(C sub(6)F sub(5)) sub(3) is found to catalyze the chemoselective hydrogenation of oxime ethers at elevated or even room temperature under 100bar dihydrogen pressure. The use of the triisopropylsilyl group as a protecting group allows for facile liberation of the free hydroxylamines. No NO cleavage: Transition-metal-free hydrogenation of oxime ethers with bulky groups at the oxygen atom (R super(3)=tBu and SiiPr sub(3)) can be achieved at mild temperatures by using the electron-deficient boron Lewis acid B(C sub(6)F sub(5)) sub(3) as a catalyst. The reduction is highly chemoselective, leaving the N--O bond intact. Subsequent fluoride-mediated cleavage of the Si--O bond (for R super(3)=SiiPr sub(3)) provides access to the free hydroxylamines (see scheme).
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ISSN:1433-7851
1521-3773
DOI:10.1002/anie.201407324