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Ethyl 2-amino-5-ethylthiophene-3- carboxylate 1, obtained from the reaction of butyraldehyde, ethyl cyanoacetate, sulfur, and triethylamine, reacted with benzoylisothiocyanate to give the corresponding ureido derivatives 2 in a high yield. Further reactions of the compound 2 with an aqueous-alcohol solution of potassium hydroxide and then with hydrochloric acid gave the 2-thio-thieno[2,3-d]pyrimidine-4-ones 3, which were reacted with RX to give novel compounds 4a-4i. Treating the compound 3 with dibromoalkane led to the formation of triacylic compounds 5j-5m. Their structures were clearly verified by IR, 1H NMR, EI-MS spectroscopy, and elemental analysis. The results of a preliminary bioassay indicated that some compounds possess excellent inhibitory activities against the root and the stalk of Brassica napus (rape) and Echinochloa crusgalli (barnyard grass) at a dosage of 100 mg/L. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file. [ABSTRACT FROM AUTHOR]

In the title compound, C21H21N3OS, the three fused rings of the 1-benzothieno[3,2- d]pyrimidine system are almost coplanar. The crystal packing is stabilized by π–π stacking inter­actions and inter­molecular C—H⋯O hydrogen bonds. [ABSTRACT FROM AUTHOR]