Quinoxalines. IX. Reaction of 2-(Halogenomethyl)-quinoxalines and -quinoline with hydroxybenzoic acids and their esters

Abstract

In the presence of a base the title compounds react to products with ether structure (4, 6), or with ester structure (3), or to structure 5 containing both functionalities in dependence on the mole ratio of the starting substances, on reaction conditions and on the substituent patterns in the hydroxybenzoic acid component. Under the influence of alkali hydroxide the m- and p-substituted compounds (6e–g) are saponified to the alkali salts of the carboxylic acid (4b, c). The o-substituted compounds (6a–d), however, are cyclized to the benzo[b]furanylquinoxalines (8). 8a, d are also obtained by thermal water elimination of the carboxylic acids 4a, d. The red-coloured benzofuranols 8 react with acetic anhydride and benzoyl-chloride/pyridine, resp., to the weakly yellow esters 9. The stucture of the products 8 and 9 is studied by UVVIS derivative spectroscopy, by theoretical calculation of the dihedral angles and by 1H and 13C NMR spectroscopy. The 1H and 13C chemical shifts are completely assigned. The quinoxalines 8a–c and the quinoline 8d only exist in the hydroxy form.