Application of Regioselective Thiophene Lithiation to the Synthesis of Thiophene Analogues of Xanthones and Thioxanthones

Article abstract of DOI:10.1021/jo00348a032

Treatment of 3-(p-tolyloxy)thiophene (3) with phenyllithium followed by carbonation with CO2 was found to be a convenient procedure for the preparation of the thiophene-2-carboxylic acid 4, which was cyclized to 5 with PPE.Treatment of 3 with butyllithium followed by carbonation gave the thiophene-2,5-dicarboxylic acid 8 which was cyclized to 9.Alkaline permanganate oxidation of 4 gave the diacid 10, which was cyclized to the tricyclic acid 11.Similar lithiation reactions were observed with additional 3-(aryloxy)thiophenes and with 3-(arylthio)thiophenes, and xanthone analogues were prepared from the resulting intermediates.