Diels-Alder Reactions of Vinyl Derivatives of (1)Benzothieno(3,2-b)Furan

摘要

2-Vinyl- (2) and 3-vinyl(1)benzothieno(3,2-b)furan (3) react with dimethyl acetylene-dicarboxylate, methyl propiolate, maleic anhydride, or acrylonitrile endo-selectively as dienes to afford new (1)benzothieno(3,2-b)(1)benzofuran derivatives 7-20. cis-Anhydrides 13 and 18 were transformed into dimethyl esters 21 and 22, respectively. It was shown that the base-catalyzed hydrolysis of 13 and 18 is accompanied by rearrangement of double bond in 13 and cis/trans isomerization of carboxylic group. Diesters 21 and 22, and nitriles 20 and 24 were aromatized by treatment with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone. Selective monodecarboxylation of (1)benzothieno(3,2-b)(1)benzofuran-8,9-dicarboxylic acid (26) and (1)benzothieno(3,2-b)(1)benzofuran-6,7-dicarboxylic acid (27) afforded (1)benzothieno(3,2-b)(1)benzofuran-8-carboxylic acid (280 and (1)benzothieno(3,2-b)(1)-benzofuran-7-carboxylic acid (29), respectively.