Vince Szabó

The reactions of chromone and 2-hydroxychromanone with hydroxylamine

Abstract Chromone and 2-hydroxychromanone react with hydroxylamine to give several products through attack at Ca2. The aldoxime 2 is transformed to dioxime 4 or to isoxazole 3 . The dioxime exists as a tautomer mixture; it reacts in several ways, giving chromoneoxime 8 , isoxazole 10 and a new isoxazoline 9 .

Stereochemical studies of 2-hydroxychromanones by 1H NMR spectroscopy

Abstract 2-Hydroxychromanones ( 2a – 2f ) were synthesized by ring closing of 2-hydroxyacetophenones ( 1a , b ) and 2-hyroxypropiophenones ( 1c – 1f ). In the case of 2-hydroxy-3-methyl-chromanones ( 2c – 2f ) a mixture of cis and trans isomers was obtained. The trans isomers are conformalionally homogeneous, the cis isomers exist in a conformational equilibrium. At room temperature the isomers are transformed into each other via opening of the heteroring. This process becomes faster in alkaline medium and the β-diketo form 4 can also be observed.

Reaction of chromones with hydroxylamine in anhydrous methanol : A novel route for the preparation of chromone oximes

Abstract The reaction of 4H-1-benzopyran-4-one (chromone, bar1 ,) 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 be also 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

Examination of the ring-chain isomerism of 2-hydroxy-chromanones with 1H NMR spectroscopy

Abstract In the cyclic derivatives (1) the hydroxyl group is of pseudo-axial orientation (1: α-anomer) and no equatorial form (1: β-anomer) has been detected. The ring-opened compound exits in keto-enol equilibrium (2 α 3) dependent of the R-substituent.

High-performance liquid chromatography of chromonoid compounds

Abstract Synthetic chromones and isoflavones have been investigated by high-performance reversed-phase partition chromatography on C8 and C18 stationary phases in the isocratic mode, using methanol—water and acetonitrile—water eluents. The effect of various substituents on the retention time and capacity ratio was studied. It has been shown that methyl and methoxyl groups increase, whereas a hydroxyl substituent decreases the value of retention time. The effects of these groups on the retention time and on the degree of separation can be predicted for chromones. Of the other substituents the 2-trifluoromethyl, 6-chloro and cyclic groups (e.g. phenyl, benzyl, thiazolyl etc.) increased the retention time while the opposite effect was observed in the case of certain nitrogen-containing (tetrazolyl, cyano, carboxamido) functions.

A new pathway in the reactions of chromones and hydroxylamine in anhydrous solutions

In the nucleophilic reaction of chromone (1) with NH2OH·HC1 in anhydrous methanol a new compound 2-methoxychromanone (6) appeared as an intermediate in the formation of chromone oxime (8) and 2-methoxychromanone oxine (7).