title: Strong deshielding in aromatic isoxazolines.
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.
authors.affiliation: P. J. Šafárik University, Faculty of Science, Institute of Chemistry, NMR Laboratory, Moyzesova 11, 040 01, Košice, Slovakia.
authors.forename: Lucia
authors.initials: L
authors.lastname: Ungvarská Maľučká
authors.affiliation: P. J. Šafárik University, Faculty of Science, Institute of Chemistry, NMR Laboratory, Moyzesova 11, 040 01, Košice, Slovakia.
authors.forename: Mária
authors.initials: M
authors.lastname: Vilková
authors.affiliation: Slovak Technical University, Faculty of Chemical and Food Technology, Department of Physical Chemistry, Radlinského 9, 812 37, Bratislava, Slovakia.
authors.forename: Jozef
authors.initials: J
authors.lastname: Kožíšek
authors.affiliation: P. J. Šafárik University, Faculty of Science, Institute of Chemistry, NMR Laboratory, Moyzesova 11, 040 01, Košice, Slovakia.
authors.forename: Ján
authors.initials: J
authors.lastname: Imrich
mesh_terms: D000166:Acridines / Q000737:chemistry; D002722:Chlorobenzenes / Q000737:chemistry; D018360:Crystallography, X-Ray; D003500:Cyclization; D007555:Isoxazoles / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D009570:Nitriles / Q000737:chemistry; D010080:Oxazoles / Q000737:chemistry*; D010456:Peptides, Cyclic / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: C572714:2,6-dichlorobenzonitrile oxide; D000166:Acridines; D002722:Chlorobenzenes; D007555:Isoxazoles; D009570:Nitriles; D010080:Oxazoles; D010456:Peptides, Cyclic; C074972:westiellamide
keywords: 1,3-dipolar cycloadditions; 13C; 1H; NMR; acridine; benzonitrile oxides; isoxazolines; regioselectivity