HETEROCYCLIC ANALOGS OF 5,12-NAPHTHACENEQUINONE 15*. SYNTHESIS OF NEW ANTHRA[2,3-<i>b</i>]THIOPHENE-3(2)-CARBOXYLIC ACIDS

Abstract

Methods have been developed for the synthesis of anthra[2,3-b]thiophene-3(2)-carboxylic acids and their derivatives through modifications of 4,11-dibutoxy-3-methylanthra[2,3-b]thiophene-5,10-dione. A scheme involving methyl group transformations was proposed for the preparation of dibutoxyanthra[2,3-b]thiophene-3-carboxylic acid, including reactions of radical halogenation, hydrolysis, and oxidation of a 3-formyl derivative. 4,11-Dihydroxy-3-methylanthra[2,3-b]thiophene-2-carboxylic acid was synthesized
from the appropriate carbonitrile, obtained by Rosenmund–von Braun reaction from 2-bromo-4,11-dibutoxy-3-methylanthra[2,3-b]thiophene-5,10-dione.