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Solid-phase Synthesis of [4.4] Spirocyclic Oximes
Published on: February 6, 2019
Knorr cyclizations and distonic superelectrophiles
Kiran Kumar Solingapuram Sai1, Thomas M Gilbert, Douglas A Klumpp
1Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, Illinois 60115, USA.
The Journal of Organic Chemistry
|November 15, 2007
Summary
Researchers explored the Knorr cyclization using experimental and theoretical methods. Beta-ketoamides form dicationic superelectrophiles, directly observed via NMR, with triflic acid proving an effective catalyst.
Area of Science:
- Organic Chemistry
- Physical Chemistry
- Reaction Mechanisms
Background:
- The Knorr cyclization is a key reaction in organic synthesis.
- Understanding its mechanism, particularly under strong acid catalysis, is crucial.
- Beta-ketoamides are common substrates whose behavior in superacidic media was not fully elucidated.
Purpose of the Study:
- To investigate the mechanism of the acid-catalyzed Knorr cyclization.
- To identify the reactive intermediates formed from beta-ketoamides in superacidic conditions.
- To evaluate the efficacy of superacids as catalysts for this reaction.
Main Methods:
- Experimental studies utilizing low-temperature Nuclear Magnetic Resonance (NMR) spectroscopy (1H, 15N, 13C).
- Theoretical calculations to support experimental observations.
- Synthetic applications using trifluoromethanesulfonic acid (CF3SO3H) as a Brønsted superacid catalyst.
Main Results:
- Beta-ketoamides, such as acetoacetanilide, undergo diprotonation at carbonyl oxygens.
- Dicationic superelectrophiles were directly observed and characterized by NMR.
- Triflic acid (CF3SO3H) demonstrated high catalytic activity in the Knorr cyclization.
Conclusions:
- The Knorr cyclization proceeds via dicationic superelectrophile intermediates.
- Superacids are effective catalysts, enabling direct observation of these reactive species.
- This study provides fundamental insights into the reaction mechanism under strongly acidic conditions.
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