Flavyliumsalts and 2-hydroxychalcones (1-phenyl-3-(2-hydroxyphenyl)-2-propen-1-ones) react with hydroxylamine in pyridine to form 2,5-dihydroisoxazoles. These undergo thermal and acid-catalyzed rearrangements to isomeric 4,5-dihydroisoxazoles and chalcone oximes, respectively. With hydrazine, flavyliumsalts yield phenolic 4,5-dihydro-3,5-diphenyl-1H-pyrazoles. Since these readily condense with acetone