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Preparation of Stable Bicyclic Aziridinium Ions and Their Ring-Opening for the Synthesis of Azaheterocycles
Published on: August 22, 2018
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Strong deshielding in aromatic isoxazolines
Lucia Ungvarská Maľučká1, Mária Vilková1, Jozef Kožíšek2
1P. J. Šafárik University, Faculty of Science, Institute of Chemistry, NMR Laboratory, Moyzesova 11, 040 01, Košice, Slovakia.
Magnetic Resonance in Chemistry : MRC
|September 15, 2015
Summary
Strong proton deshielding was observed in novel isoxazoline regioisomers. These compounds, derived from acridinyl dipolarophiles and benzonitrile oxides, show regioselectivity influenced by reactant properties.
Area of Science:
- Organic Chemistry
- Heterocyclic Chemistry
- Spectroscopy
Background:
- Isoxazolines are important heterocyclic compounds with diverse applications.
- Acridine derivatives are known for their unique electronic and photophysical properties.
- Understanding regioselectivity in cycloaddition reactions is crucial for synthetic control.
Purpose of the Study:
- To synthesize and characterize novel di/tri-aromatic isoxazoline regioisomers.
- To investigate the influence of dipolarophile and dipole structure on regioselectivity.
- To explore the chemical reactivity of the synthesized isoxazolines.
Main Methods:
- 1,3-Dipolar cycloaddition reactions between acridin-4-yl substituted alkenes and stable benzonitrile oxides (BNOs).
- Structural elucidation using Nuclear Magnetic Resonance (NMR), Mass Spectrometry (MS), and X-ray crystallography.
- Analysis of regioselectivity based on the position of the acridine moiety (C-4 or C-5).
Main Results:
- Synthesis of pairs of 4-acridinyl (4-Acr) and 5-acridinyl (5-Acr) isoxazoline regioisomers.
- Regioselectivity was found to be dependent on the electronic nature of both the dipolarophile (ester, amide, styrene) and the BNO dipole.
- The styrene dipolarophile predominantly yielded 4-Acr isomers, while 2,4,6-trimethoxy-BNO favored 5-Acr products.
- Basic hydrolysis of an amide cycloadduct resulted in an unexpected isoxazolone.
Conclusions:
- The study successfully synthesized and characterized new isoxazoline regioisomers.
- A detailed understanding of regioselectivity in these cycloaddition reactions was achieved.
- The findings provide valuable insights for the rational design of heterocyclic compounds with specific substitution patterns.
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