Synthesis of [1]Benzothieno[3,2- b][1]benzothiophene Derivatives via Successive Iodocyclization/Photocyclization of
Tsugio Kitamura1, Kazuhiro Morita1, Haruka Nakamori1
1Department of Chemistry and Applied Chemistry , Saga University , Honjo-machi , Saga 840-8502 , Japan.
Abstract:
A new synthetic method for [1]benzothieno[3,2- b][1]benzothiophene derivatives (BTBTs) was developed. The present method consists of iodocyclization of 1,2-bis(2-methylthiophenyl)ethynes and photolysis of 3-iodo-(2-methylthiophenyl)benzo[ b]thiophenes. With 1,2-bis(2-methylthiophenyl)ethynes treated with I2/PhI(OAc)2 in CH2Cl2 at room temperature, selective cyclization at sulfur took place to give 3-iodo-(2-methylthiophenyl)benzo[ b]thiophenes in good yields. Irradiation of the iodinated benzo[ b]thiophenes with a high-pressure Hg lamp (>290 nm) provided BTBTs in good yields. Furthermore, the present method was applied to the synthesis of bis[1]benzothieno[2,3- d;2',3'- d']benzo[1,2- b;4,5- b']dithiophene (BBTBDT).
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