V. Sosnovskikh, V. Moshkin, M. Kodess
Aug 18, 2008
Citations
1
Influential Citations
37
Citations
Journal
Tetrahedron
Abstract
Abstract Reaction of 3-(polyfluoroacyl)chromones with hydroxylamine free base proceeds via nucleophilic 1,4-addition followed by opening of the pyrone ring and subsequent cyclization to 4-(polyfluoroalkyl)-4 H -chromeno[3,4- d ]isoxazol-4-ols in good yields. On treatment with trifluoroacetic acid, the isoxazole ring of this annulated heterocyclic system opens to give 3-cyano-2-(polyfluoroalkyl)chromones, which were successfully hydrolyzed with concentrated H 2 SO 4 to afford 3-carbamoyl-2-(polyfluoroalkyl)chromones. On the other hand, oximation of 3-(polyfluoroacyl)chromones with hydroxylamine hydrochloride occurs either at the carbonyl carbon atom connected to the R F group or at the C-2 atom to give 3-R F C( NOH)-chromones and 5-R F -4-salicyloylisoxazole oximes, respectively. The former were easily converted to 3-R F -4-salicyloylisoxazoles by simple heating in dimethyl sulfoxide.