Spiropyrazolines from tandem reaction of azides and alkyl vinyl ketones

Yang, Chia-Hsi; Lee, Lang-Tone; Yang, Jun-Hao; Wang, Yu; Lee, Gene‐Hsiang

doi:10.1016/s0040-4020(01)89566-1

Cited by 20 publications

(10 citation statements)

References 9 publications

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“…The resulting ammonium salt then can facilitate proton transfer to the distal nitrogen, leading to fragmentation and forming diazo compound 6 . Intermediate 6 can undergo an intramolecular cycloaddition between the diazo and alkene to afford compound 3 . , Alternatively, in the presence of excess acrylate, diazo 6 can intercept a second equivalent of acrylate to form product 7 . ,,, To mitigate this side product, a second procedure was developed for products where the intramolecular cyclization was slow (Table ). The triazoline was preformed by mixing the azide and acrylate neat at room temperature.…”

Section: Resultsmentioning

confidence: 99%

A Cascade Reaction of Cinnamyl Azides with Acrylates Directly Generates Tetrahydro-Pyrrolo-Pyrazole Heterocycles

2020

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Developing reactions to generate complex and modular building blocks in a concise and direct fashion remains a contemporary synthetic challenge. This work describes a stereoselective cascade reaction between allylic azides and acrylates that directly generates tetrahydro-pyrrolo-pyrazole ring systems. These products contain up to four contiguous stereocenters, two of which may be tetrasubstituted carbon atoms attached to a nitrogen atom.Over 30 examples are provided with an average isolated yield of 71% (ranging from 40% to 94%). The reaction was easily scaled to use more than one gram of starting material, and the products can be readily diversified.

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Section: Resultsmentioning

confidence: 99%

A Cascade Reaction of Cinnamyl Azides with Acrylates Directly Generates Tetrahydro-Pyrrolo-Pyrazole Heterocycles

2020

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“…A general description on metal alkene coordination is made using Dewar Chat‐Duncanson model 7 . Though there are reports on copper mediated azide‐alkene reaction resulting in triazolines, 23‐30 the mechanism of this reaction has not been reported previously. The π‐bond consists of two components: one is arising from overlapping of the occupied olefin π orbital and the unoccupied 4s 0 orbital of the Cu (I) atom which is dominant in the bond, and the other is formed by the back donation from the 3d 10 Cu(I) orbitals to the unoccupied antibonding orbital of the alkene‐group.…”

Section: Resultsmentioning

confidence: 99%

Facile crosslinking of polybutadienes via triazoline heterocyclics: Deciphering mechanism and structural‐property relations

Reshmi

Periya

Chinthalapalli

et al. 2020

Polymers for Advanced Techs

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Chain-end functionalized polybutadiene polymers have widespread application in composite solid propellants (CSP). Curing of these polymers is effected using the reactions at the terminal groups with isocyanates or aziridines if the functional groups are hydroxyl or carboxyl respectively. The high toxicity of isocyanates and aziridines demands alternate cure methods. A facile reaction, devoid of any side reactions is the most desirable one. The large number of double bonds in polybutadienes is favorable for 1, 3-dipolar addition reaction with an azide to yield triazolines. The mechanistic aspects of the uncatalyzed and copper-mediated azide-alkene reaction have not been explored previously. The present study focuses on elucidation of the reaction using model compounds of polybutadiene namely trans 3-hexene, cis-3 hexene and 3-methyl pentene which mimic the microstructure of polybutadienes. The paper presents the elucidation of the mechanism using density functional theory (DFT) calculations, detailed reaction pathway and its experimental validation using Fourier transform infrared (FTIR) spectroscopy and 13 C nuclear magnetic resonance (NMR) spectroscopy. DFT studies indicate that the activation barrier of 63.8 to 85 kJ/mol for the uncatalyzed reaction. In the copper catalyzed reaction, it diminishes to the range of 18.1 to 33.0 kJ/mol. The thermal decomposition aspects of the cured triazoline system were evaluated using thermogravimetric-mass spectrometer (TG-MS). The binder undergoes single stage decomposition in the temperature regime of 278 C-534 C which is lower than that reported for polyurethane-polybutadienes. The decomposition reaction yields more volatile products like nitrogen, carbon dioxide, 1,4 butadiene and 4-vinylcyclohexene, conducive for propellant applications.

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“…138,139 Yang performed a cycloaddition with acrylonitrile (Scheme 2b). [140][141][142] The initially formed triazoline adduct rearranged to form the observed fused ring system. This rearrangement is particularly interesting because it requires a proximal alkene in the starting material.…”

Section: Allyl Azidementioning

confidence: 99%