The involvement of 1,3-dipolar cycloaddition (1,3-DP), double bond migration, metathesis, and nitrile oxide (including in situ-generated nitrile oxide) as dipoles, together with the C=C bond containing dipolarophiles, in the syntheses of 2-isoxazolines is presented. Methods for synthesizing isoxazolines (other than 1,3-DP cycloaddition) were also presented briefly. Various methods of nitrile oxide preparation, especially in situ-generated procedures, are presented. Special attention was paid to the application of various combinations of 1,3-DP cycloaddition with double bond migration (DBM) and with alkene metathesis (AM) in the syntheses of trisubstituted isoxazolines. Allyl compounds of the type QCH2CH=CH2 (Q = ArO, ArS, Ar, and others) play the role of dipolarophile precursors in the combinations of DPC mentioned, DBM and AM. Mechanistic aspects of cycloadditions, i.e., concerted or stepwise reaction mechanism and their regio- and stereoselectivity are also discussed from experimental and theoretical points of view. Side reactions accompanying cycloaddition, especially nitrile oxide dimerization, are considered. 2-Isoxazoline applications in organic synthesis and their biological activity, broad utility in medicine, agriculture, and other fields were also raised. Some remaining challenges in the field of 1,3-DP cycloaddition in the syntheses of isoxazolines are finally discussed.
Keywords: 1,3-dipolar cycloaddition; 2-isoxazolines; allyl compounds; isoxazolines in agriculture; isoxazolines in organic synthesis; isoxazolines in pharmacy; nitrile oxide; reaction mechanism; syntheses.