Unambiguous structure elucidation of the reaction products of 3-acyl-4-methoxy-1-methylquinolinones with hydroxylamine via NMR spectroscopy

Reaction of 3-acyl-4-methoxy-1-methylquinolinones 2a, b with hydroxylamine has been investigated under different experimental conditions. Whereas compound 2a gives rise selectively and exclusively to the regioisomeric isoxazolo[4,5-c]-or isoxazolo[4,3-c] quinolin4(5H) one (compound 3a or 4a, respectively), reaction of 2b always led to a mixture of the required isoxazole together with the oxazole derivative. Structural elucidation of all products has been independently achieved by multinuclear (C-13 and N-15) magnetic resonance spectroscopy. (c) 2007 Elsevier Ltd. All rights reserved.