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■ Synthesis of 2-Substituted 3-(2-benzo[b]thienyl)- or 3-(2-Thienyl)-3-methylthioacrylonitriles

Shinichi Fukuda, Yoshinori Tominaga, Yoshiro Matsuda, and Goro Kobayashi

*Faculty of Pharmaceutical Sciences, Nagasaki University, 1-14, Bunkyo-machi, Nagasaki 852-8521, Japan

Abstract

Reaction of methyl benzo[b]thiophene-2-dithiocarboxylate(2) with active methylene compounds (malononitrile, methyl cyanoacetate and cyanoacetamide) in the presence of sodium hydride followed by methylation with dimethyl sulfate gave the corresponding 2-substituted 3-(2-benzo[b]thienyl)-3-methylthioacrylonitriles (2-CN, 2-COOCH₃, and 2-CONH₂) (3a, b, c) in good yields. Compounds 3a and 3b were alternatively synthesized by the reaction of 2-lithiobenzo[b]thiophene with ketenethioacetal [bis(methylthio)methylenemalononitrile and methyl bis (methylthio)methylenecyanoacetate]. Similarly, 2-cyano-3-methylthio-3-(2-thienyl)acrylonitrile (6) was also prepared from methyl thiophene-2-dithiocarboxylate(5). Methyl dithiocarboxylates (2 and 5) were prepared by the reaction of 2-lithio derivatives of 1 and 4 with carbon disulfide followed by methylation with dimethyl sulfate in good yields.