REACTION OF CHROMONES WITH HYDROXYLAMINE IN ANHYDROUS METHANOL. A NOVEL ROUTE FOR THE PREPARATION OF CHROMONE OXIMES

Article abstract of DOI:10.1016/S0040-4020(01)87646-8

The reaction of 4H-1-benzopyran-4-one (chromone, 1) and its substituted derivatives with hydroxylamine in aqueous alcohols gives isoxazoles 5, and 10, as the major products, whereas 1a is transformed mainly into 8a with hydroxylamine hydrochloride in anhydrous methanol; compounds 5a, 9a and 10a can also be isolated, and the formation of 6a and 7a has been detected, as well.Depending on the character of the substituent, substituted chromones 1b-g afforded 7, 8 or 9 as the isolable major product.Based on the present experiments compound 6, produced in an acid-catalyzed methanol addition on 1, is regarded the key intermediate of the formation of chromone oxime