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Kinetic studies of inverse electron demand Diels-Alder reactions (iEDDA) of norbornenes and 3,6-dipyridin-2-yl-1,2,4,5-tetrazine.

Knall AC, Hollauf M, Slugovc C - Tetrahedron Lett. (2014)

Bottom Line: Norbornenes are, due to their straightforward synthetic availability, especially interesting in the latter context.Therefore, the reactivity of different norbornene-based compounds was compared with unsubstituted norbornene and other alkenes using UV-vis measurements for the determination of reaction rates under pseudo first order conditions.Thereby, exo,exo-5-norbornene-2,3-dimethanol was found to be almost as reactive as unsubstituted norbornene whereas (±)-endo,exo-dimethyl-5-norbornene-2,3-dicarboxylate reacted only insignificanty faster than unstrained alkenes.

View Article: PubMed Central - PubMed

Affiliation: Institute for Chemistry and Technology of Materials (ICTM), Graz University of Technology, Stremayrgasse 9, A-8010 Graz, Austria.

ABSTRACT
Inverse electron demand Diels-Alder additions (iEDDA) between 1,2,4,5-tetrazines and olefins have recently found widespread application as a novel 'click chemistry' scheme and as a mild technique for the modification of materials. Norbornenes are, due to their straightforward synthetic availability, especially interesting in the latter context. Therefore, the reactivity of different norbornene-based compounds was compared with unsubstituted norbornene and other alkenes using UV-vis measurements for the determination of reaction rates under pseudo first order conditions. Thereby, exo,exo-5-norbornene-2,3-dimethanol was found to be almost as reactive as unsubstituted norbornene whereas (±)-endo,exo-dimethyl-5-norbornene-2,3-dicarboxylate reacted only insignificanty faster than unstrained alkenes.

No MeSH data available.


Related in: MedlinePlus

Inverse electron demand Diels–Alder (iEDDA) reaction leading to the formation of pyridazines.
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f0020: Inverse electron demand Diels–Alder (iEDDA) reaction leading to the formation of pyridazines.

Mentions: Inverse electron demand Diels–Alder additions (iEDDA) are known to take place between 1,2,4,5-tetrazines and olefins. Thereby, a bicyclic intermediate A is formed which readily eliminates nitrogen and rearranges resulting in dihydropyridazines (B), which may be further oxidized to pyridazines (C, Scheme 1). In contrast to Diels–Alder reactions with ‘normal’ electron demand, the HOMO of the dienophile and the LUMO of the diene interact in iEDDA reactions.1 Therefore, while electron-deficient tetrazines react faster due to a lowered LUMO, the olefinic dienophiles should ideally be electron-rich. Additionally, substituents which are sterically hindering on either reaction partner were found to reduce the reaction rate. Furthermore, strained double bonds are known to react faster in iEDDA reactions.2 While these general rules apply for both alkenes and alkynes, alkynes were found to generally react slower in iEDDA reactions, but directly lead to pyridazines as reaction products.


Kinetic studies of inverse electron demand Diels-Alder reactions (iEDDA) of norbornenes and 3,6-dipyridin-2-yl-1,2,4,5-tetrazine.

Knall AC, Hollauf M, Slugovc C - Tetrahedron Lett. (2014)

Inverse electron demand Diels–Alder (iEDDA) reaction leading to the formation of pyridazines.
© Copyright Policy - CC BY
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4125744&req=5

f0020: Inverse electron demand Diels–Alder (iEDDA) reaction leading to the formation of pyridazines.
Mentions: Inverse electron demand Diels–Alder additions (iEDDA) are known to take place between 1,2,4,5-tetrazines and olefins. Thereby, a bicyclic intermediate A is formed which readily eliminates nitrogen and rearranges resulting in dihydropyridazines (B), which may be further oxidized to pyridazines (C, Scheme 1). In contrast to Diels–Alder reactions with ‘normal’ electron demand, the HOMO of the dienophile and the LUMO of the diene interact in iEDDA reactions.1 Therefore, while electron-deficient tetrazines react faster due to a lowered LUMO, the olefinic dienophiles should ideally be electron-rich. Additionally, substituents which are sterically hindering on either reaction partner were found to reduce the reaction rate. Furthermore, strained double bonds are known to react faster in iEDDA reactions.2 While these general rules apply for both alkenes and alkynes, alkynes were found to generally react slower in iEDDA reactions, but directly lead to pyridazines as reaction products.

Bottom Line: Norbornenes are, due to their straightforward synthetic availability, especially interesting in the latter context.Therefore, the reactivity of different norbornene-based compounds was compared with unsubstituted norbornene and other alkenes using UV-vis measurements for the determination of reaction rates under pseudo first order conditions.Thereby, exo,exo-5-norbornene-2,3-dimethanol was found to be almost as reactive as unsubstituted norbornene whereas (±)-endo,exo-dimethyl-5-norbornene-2,3-dicarboxylate reacted only insignificanty faster than unstrained alkenes.

View Article: PubMed Central - PubMed

Affiliation: Institute for Chemistry and Technology of Materials (ICTM), Graz University of Technology, Stremayrgasse 9, A-8010 Graz, Austria.

ABSTRACT
Inverse electron demand Diels-Alder additions (iEDDA) between 1,2,4,5-tetrazines and olefins have recently found widespread application as a novel 'click chemistry' scheme and as a mild technique for the modification of materials. Norbornenes are, due to their straightforward synthetic availability, especially interesting in the latter context. Therefore, the reactivity of different norbornene-based compounds was compared with unsubstituted norbornene and other alkenes using UV-vis measurements for the determination of reaction rates under pseudo first order conditions. Thereby, exo,exo-5-norbornene-2,3-dimethanol was found to be almost as reactive as unsubstituted norbornene whereas (±)-endo,exo-dimethyl-5-norbornene-2,3-dicarboxylate reacted only insignificanty faster than unstrained alkenes.

No MeSH data available.


Related in: MedlinePlus