A carbon-13 Nmr assignment study of 3,5-diarylisoxazoles

The assignment of the carbon-13 nmr resonances of 3-(aryl)-5-phenylisoxazoles (I) and 3-phenyl-5-(aryl)-isoxazoles (II) in dimethylsulfoxide-d₆ has been made. The assignments were made by using model compounds, chemical shift arguments, coupling with fluorine substituents, and shifts resulting from quaternization of the isoxazole ring. A carbon-13 nmr method for distinguishing between I and II which can be produced simultaneously by certain synthetic methods is presented.