Cyclopentadienones via a tandem C-cyclopropylnitrone cyclization-cycloreversion sequence.
Ihsan Erden1, Christian Gärtner1, Jingxiang Ma1
1Department of Chemistry and Biochemistry, San Francisco State University, 1600 Holloway Avenue, San Francisco, CA 94132, USA.
European Journal of Organic Chemistry
|December 5, 2017
Summary
Spirocyclic nitrones undergo a unique cyclization-cycloreversion cascade, yielding cyclopentadienones. Spiroconjugation in the cyclopropane ring enhances reactivity, proving essential for this transformation.
Area of Science:
- Organic Chemistry
- Synthetic Chemistry
- Reaction Mechanisms
Background:
- Nitrones are versatile intermediates in organic synthesis.
- Spirocyclic compounds offer unique structural and electronic properties.
- Cyclopropane rings can exhibit enhanced reactivity due to strain and electronic effects.
Purpose of the Study:
- To investigate the reactivity of aldonitrones derived from spiro[2.4]hepta-4,6-diene and its benzo analog.
- To explore the mechanism of tandem cyclization-cycloreversion reactions.
- To elucidate the role of spiroconjugation in enhancing cyclopropane reactivity.
Main Methods:
- Synthesis of spirocyclic aldonitrones and NH-nitrones.
- Uncatalyzed tandem intramolecular cyclization-cycloreversion reactions.
- Density Functional Theory (DFT) calculations.
- Control experiments with dihydro and tetrahydro derivatives.
Main Results:
- Spirocyclic nitrones efficiently transform into cyclopentadienones via a tandem reaction.
- The reaction proceeds through a cyclopropane-nitrone cyclization followed by 5,6-dihydro-1,2-oxazine cycloreversion.
- DFT calculations support a concerted, highly asynchronous reaction pathway.
- The spirocyclopentadiene moiety is crucial for the reaction's success, highlighting spiroconjugative effects.
Conclusions:
- A novel synthetic route to cyclopentadienones from spirocyclic nitrones has been established.
- The reaction mechanism involves a unique cascade of cyclization and cycloreversion.
- Spiroconjugation plays a significant role in activating the cyclopropane ring for this transformation.
![Solid-phase Synthesis of [4.4] Spirocyclic Oximes](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2FCDNSource%2Fteasers%2F58508.jpg&w=3840&q=50)
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