Einfache Herstellung von zum Teil in 5,6-Stellung anellierten 2-Amino-thieno [2,3-d][1,3]thiazin-4-onen

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Abstract
The Facile Synthesis of 2-Aminothieno[2,3-d][1,3]thiazin-4-ones, in Some Cases 5,6-Anellated The cyclization of ethyl 2-thioureidothiophene-3-carboxylates is known to give 2-thioxothieno[2,3-d]pyrimidin-4-ones not only under basic conditions but also upon treatment with ethanolic hydrochloric acid. On the other hand, we have found that ethyl 2-thioureidothiophene-3-carboxylates 1 on treatment with concentrated sulphuric acid, polyphosphoric acid or anhydrous perchloric acid undergo cyclocondensation to give 2-aminothieno[2,3-d][1,3]thiazin-4-ones 2a-2r. Reaction of 2 with phosphorus (V) sulfide yielded the thieno[2,3-d][1,3]thiazine-4-thiones 3b and 3c; ring cleavage of the aminothienothiazinones 2k, 2m, 2n with diluted sodium hydroxide gave the 2-thioureidothiophene-3-carboxylic acids 5k, 5m, 5n, respectively.

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