Donor-substituted nitrocyclopropanes: immediate ring-enlargement to cyclic nitronates
Christian D Schmidt1, Johannes Kaschel, Tobias F Schneider
1Institut für Organische Chemie, Technische Universität Braunschweig , Hagenring 30, D-38106 Braunschweig, Germany.
Organic Letters
|November 13, 2013
Summary
Donor-substituted alkenes reacted with nitro diazo ethyl acetate under rhodium catalysis, forming nitrocyclopropanes. Ring enlargement occurred with strong electron donors, yielding cyclic nitronates rather than ketene acetals.
Area of Science:
- Organic Chemistry
- Catalysis
- Reaction Mechanisms
Background:
- Donor-substituted alkenes are versatile building blocks in organic synthesis.
- Rhodium-catalyzed reactions offer efficient pathways for complex molecule construction.
- Diazo compounds serve as key precursors in various catalytic transformations.
Purpose of the Study:
- To investigate the rhodium-catalyzed reaction of donor-substituted alkenes with α-diazo-α-nitro ethyl acetate.
- To elucidate the mechanism of nitrocyclopropane formation and subsequent transformations.
- To explore the influence of electron-donating substituents on the reaction outcome.
Main Methods:
- Rhodium-catalyzed cyclopropanation reaction.
- In situ generation of nitrocyclopropanes.
- Analysis of reaction products using spectroscopic techniques.
- Density Functional Theory (DFT) calculations to study reaction pathways.
Main Results:
- Nitrocyclopropanes with a geminal ester functionality were successfully synthesized.
- Strong electron donors induced ring-enlargement of the nitrocyclopropanes.
- The nitro group was incorporated into the ring, forming cyclic nitronates.
- The ester moiety was excluded from the cyclic product.
- DFT studies confirmed kinetic and thermodynamic preference for cyclic nitronate formation over cyclic ketene acetals.
Conclusions:
- The rhodium-catalyzed reaction provides a novel route to cyclic nitronates from donor-substituted alkenes and α-diazo-α-nitro ethyl acetate.
- Electron-donating substituents play a crucial role in directing the reaction towards ring enlargement.
- Cyclic nitronates are the favored products due to both kinetic and thermodynamic control, as supported by computational studies.
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