New convenient methods for the synthesis of 1,2,3-thiadiazole, 1,3,4-thiadiazine, and 1,2,5-triazepine derivatives are reported. In the heterocyclization process, the reactivity of 1-thia-4-aza-1,3-butadiene system of syn-2-phenylhydrazono-3-oxothiobutanoic acid anilides was exploited.The structure and chemistry of the 1,2,3-thiadiazole system have been under active investigation for years. 1-3 Its derivatives are useful in the treatment of hyperproliferative disorders including tumor growth and angiogenesis, and lymphoproliferative symptoms. 4 Moreover, derivatives of this system are applied in the treatment and/or prevention of morbid states mediated by oxytocin, including premature labour and dysmenorhea. 5 The 1,2,3-thiadiazole moiety is crucial for the antibacterial activity of new carbapenems 6 as well as for the efficacy of some pesticides. 7 The biological activity of 1,2,5-triazepines 8 has received less attention than the corresponding benzofused system.Recently, we have reported 9,10 the synthesis of 1,3-and 1,4-diazines which used the C-2 disubstituted thioanilides of 3-oxobutanoic acid 1 (X = S) 11 in heterocyclization reactions with various diamines. We have found that good leaving groups at C-2 of compound 1 offer an entry to formation of six-and seven-membered rings by treatment with binucleophiles. The reaction includes the initial nucleophilic attack of the nitrogen atoms of aliphatic 1,3-or 1,4-diamines on C-2 of compounds 1, followed by a novel sigmatropic rearrangement. On the other hand, the reactions of 1 with aliphatic 1,2-diamines lead to 1,4-diazines by ring expansion of the intermediate 1, 3-diazines. 12 In order to develop synthetic applications of thioanilides 1a-c in closing heterocyclic rings we have transformed them into phenylhydrazones 2a-c by treatment with phenylhydrazine (Scheme 1). The nucleophilic attack of the amino group of phenylhydrazine took place exclusively on the C-2 position of 2-anilino-2-methoxy-3-oxothiobutanoic acid anilides 1a-c.In contrast, the reaction of 2-anilino-2-methoxy-3-oxobutanoic acid anilide 3a (X = O), under similar conditions, exclusively provided osazone 4a (Scheme 1).Compounds 2a-c can appear in two isomeric forms corresponding to Z or E configuration of the 1-thia-4-aza-1,3-butadiene system. In solution, spectral data confirm the structure of the molecules of 2a-c as shown in Scheme 1 as the unique reaction product. X-ray analysis of 2a was carried out to prove the configuration in the solid state and precisely determine the molecular geometry. 14 A perspective view of molecule of 2a with the crystallographic atom numbering is presented in Figure 1. The central framework of the molecule, consisting of heteroatoms (S1, O1, N1-N3) and carbon atoms C1-C4, is quite flat. None of these atoms deviates from the least-squares plane passing through the heteroatoms by more than 0.1
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