The 2-acylcycloalkanones 1a-g and 3a-c, possessing a polyfluoroalkyl group. react with hydroxylamine regio- and stereoselectively to yield 4,5-dihydroisoxazol-5-ols 2a-g and 4a-c, respectively i.e., products of N-addition to the oxo group at the cycloalkane ring (Schemes 1 and 2). The products 2 and 4 can be dehydrated under drastic conditions only (Schemes 3 and 4). The structure of one of the 4,5-dihydroisoxazol-5-ols was confirmed by X-ray crystal-structure analysis.
Symmetrical and unsymmetrical bis-fluoroacylcyclopentanones and cyclohexanones were synthesized. NMR data reveal that the keto-enol tautomeric equilibrium is changed markedly by the presence of a trimethylene bridge compared to an ethylene moiety. A considerable influence of the fluoroalkyl chain length was found for 2,6-(bisfluoroacyl)cyclohexanones. (C) 2003 Elsevier B.V. All rights reserved.