Addition and cyclisation reactions of sugar phenylhydrazone derivatives via a 1,4-elimination process: preparation of 3-(2-acetamido-1-phenylhydrazonobutyl)-2(1 H)-quinoxalinone and 3-(1-acetamidopropyl)-pyrazolo[3,4- b]quinoxaline (flavazole) derivatives

Abstract

Acetylation of 3( l- threo-2,3,4-trihydroxy-1-phenylhydrazonobutyl)-2(1 H)-quinoxalinone derivaties ( 1a and 1c) and of the d- erythro diastereomers ( 1b and 1d), prepared from l-ascorbig acid and d-isoascorbic acid, respectively, and then treatment of the products ( 1h– 1k) with methanolic ammonia gave enantiomeric 3-(2-acetamido-3,4-dihydroxy-1-phenylhydrazonobutyl)-2-(1 H)-quinoxalinone derivatives ( 3a– 3d) with unidentified configuration at C-2′ via a stereoselective nocleophilic 1,4-addition reaction to the transiently formed phenylazoene groups. The quinoxalinone derivatives with a free NH-1 group (e.g., 3a and 3b) were dehydrocyclised to give the corresponding acetamidodeoxypyrazolo-quinoxalines (flavazoles, 4a and 4b). The phenyl group of the quinoxaline derivatives 1h– 1j could be nitrated selectively to give the corresponding p-nitrophenylhydrazones. 1f and 1g. Thermolysis of 1h afforded a pyrazolylquinoxaline derivative ( 2b).