Strong deshielding in aromatic isoxazolines |
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| Authors: | Lucia Ungvarská Ma?u?ká Mária Vilková Jozef Ko?í?ek Ján Imrich |
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| Institution: | 1. P. J. ?afárik University, Faculty of Science, Institute of Chemistry, NMR Laboratory, Ko?ice, Slovakia;2. Slovak Technical University, Faculty of Chemical and Food Technology, Department of Physical Chemistry, Bratislava, Slovakia |
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| Abstract: | Very strong proton deshielding was found in di/tri‐aromatic isoxazoline regioisomers prepared from acridin‐4‐yl dipolarophiles and stable benzonitrile oxides (BNO). Three alkenes, (acridin‐4‐yl)‐CH?CH‐R (R = COOCH3, Ph, and CONH2), reacted with three BNO dipoles (2,4,6‐trimethoxy, 2,4,6‐trimethyl, 2,6‐dichloro) to give pairs of target isoxazolines with acridine bound to C‐4 or C‐5 carbon of the isoxazoline (denoted as 4‐Acr or 5‐Acr). Regioselectivity was dependent on both the dipolarophile and dipole character. The ester and amide dipolarophile displayed variable regioselectivity in cycloadditions whereas the styrene one afforded prevailing 4‐Acr regioisomers. 2,4,6‐Trimethoxy‐BNO was most prone to form 5‐Acr isoxazolines while mesitonitrile oxide gave major 4‐Acr isoxazolines. Basic hydrolysis of the amide cycloadduct led to an unexpected isoxazolone product. The structure of the target compounds was studied by NMR, MS, and X‐ray crystallography. Copyright © 2015 John Wiley & Sons, Ltd. |
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| Keywords: | NMR 1H 13C 1 3‐dipolar cycloadditions regioselectivity acridine benzonitrile oxides isoxazolines |
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