A Facile Synthesis of Fluoroalkylisoxazoles

Reaction of benzohydroximinoyl chlorides and β‐(trifluoromethyl)‐acetylenic esters: Synthesis of regioisomeric (trifluoromethyl)‐isoxazolecarboxylate esters and oxime addition products

“…Trifluoromethylisoxazoles have been prepared by cyclocondensation of hydroxylamine and conjugated ynone [9], β-diketones [10,11] or difluoroalkyl-2-iodoalkenes [12] or by 1,3-dipolar cycloadditions of nitrile oxides and trifluoromethyl substituted dipolarophiles such as pyrrolidinoacrylates [13], β-ketoesters [14] and acetylenic esters [15][16][17]. The cyclocondensation routes provide 3-and 5-trifluoromethylisoxazoles depending on the conditions employed.…”

“…Trisubstituted isoxazoles can be prepared directly by dipolar cycloadditions, which give 5-trifluoromethyl isomers as the major product from addition of nitrile oxides to perfluoroalkyl substituted β-ketoesters, acetylenes and acrylates. Small amounts (5 -10%) of the regioisomeric 4-trifluoromethylisoxazoles have been proposed based on the analysis of crude reaction mixtures, however these minor products have not been previously isolated or characterized [15,18]. A notable exception is the addition of 1aryl-3-trifluoromethylacetylenes to nitrile oxides which gives 4-trifluoromethylisoxazoles as the major product [19].…”

Synthesis and Herbicidal Activity of 3-Aryl-5-(haloalkyl)-4-isoxazolecarboxamides and Their Derivatives

“…mp 43-45 °C (Franz and Howe, 1980).0 Lit. mp 41-42 °C (Shen et al, 1985). Scheme 4 cycloaddition (Scheme 1; Table 1).…”

“…Disubstituted 3-phenyl-5-(trifluoromethyl)isoxazoles have been obtained by cyclocondensation of a diketone and hydroxylamine (Carr et al, 1977); however, to our knowledge, the analogous trisubstituted 4-isoxazolecarboxylates have not been prepared by cyclocondensation. A few 3-aryl-5-(trifluoromethyl)-4-isoxazolecarboxylate esters had been previously prepared by 1,3-dipolar cycloadditions (Shen et al, 1985); however, none of the carboxamide derivatives were prepared, and the herbicidal activity was not described.…”

Synthesis of heterocycles with polyfluoroalkyl substituents from unsaturated compounds containing polyfluoroalkyl groups. (Review)

“…bipolar cycloaddition of aromatic nitrile oxides and polyfluoroalkyl acetylene derivatives it is possible to synthesize polyfluoroalkylisoxazoles 124 and 125[93]. The ratio of the isomers 124 and 125 amounts to ~90:124 and 125, R, n, X (total yield, %): H, 1, F (92); H, 2, F (94);…”