[One-step synthesis of 2-aminothieno [2,3-d]thiazen-4-ones in some cases 5,6-anellated from ethyl 2-benzoylthioureidothiophen-3-carboxylates and evaluation of their anti-allergy activity].

The cyclization of ethyl 2-benzoylthioureidothiophen-3-carboxylates under basic conditions is known to give 2-thioxothieno[2,3-d]pyrimidin-4(1H, 3H)-ones. On the other hand, we have found that ethyl 2-benzoylthioureidothiophen-3-carboxylates 10-16 on treatment with concentrated sulphuric acid or polyphosphoric acid/ethanol undergo cyclization to give the new 2-aminothieno[2,3-d][1,3]thiazin-4-ones 17-23, in some cases 5,6-anellated. Reaction of 10-16, which are readily available from ethyl 2-aminothiophen-3-carboxylates 3-9 and benzoyl isothiocyante affords the title compounds 17-23 in good yields. Mass spectral fragmentation of 17-23 is discussed. A series of 2-aminothieno[2,3-d][1,3]thiazin-4-ones, which contain a free or substituted amino group was evaluated in the rat active cutaneous anaphylaxis test for anti-allergy activity. One compound, 23 had weak activity in the range of theophylline. Only high concentrations of this compound inhibited weakly the histamine release from rat peritoneal mast cells activated by protamine sulfate.