Photodecomposition of tris(benzotrizol-1-yl)methane (1) in benzene gives [1-benzotryazol-1-yl-methylidene]-biphenyl-2-ylamine (2) resulting from the loss of the benzotriazolyl radical and nitrogen followed by addition of benzene. Elimination of the second benzotriazolyl radical from 2 provides the biphenyl-2-ylmethyleneamine radical, which affords phenantridine (3) after ring closure. In contrast, the photolysis of 1 in methanol gives a high yield of benzotriazole (4).
Base-promoted transformation of 4-(3-nitroaryl)-1,2,3-selenadiazoles via intermediate formation of eneselenolates followed by 5-exo-trig cyclization is reported. The regiochemistry of the intramolecular cyclization is condition-dependent. In the presence of an oxidant, the oxidative nucleophilic substitution of the hydrogen (ONSH, S(N)Ar(H)) pathway, by oxidative aromatization of the rapidly formed σ(H)-adduct, takes place. In the absence of oxidant, the reaction proceeds via intermediate formation of the σ(Cl)-adduct, following nucleophilic aromatic substitution of the halogen (S(N)Ar(Cl)) pathway.
4-(2-Chloro-5-nitrophenyl)-1,2,3-thiadiazole undergoes ring opening to produce a thioketene intermediate that reacts with an O- or N-nucleophile, forming an ester or an amide of the aryl-substituted thioacetic acid. Intermolecular cyclization of the thioacetic acid derivative via nucleophilic substitution of halogen in the aromatic ring gives an N-substituted indole-2-thiol (in case of an N-nucleophile) or a 2-alkoxy-substituted benzo[b]thiophene (in case of an O-nucleophile). The reaction is also applicable to the synthesis of heterocyclic analogues of N-substituted indole-2-thiols: 1-butyl-1,3-dihydropyrrolo[2,3-b]pyridine-2-thione was synthesized as an example. In the presence of potassium thioacetate (an S-nucleophile) 4-nitro-2-(1,2,3-thiadiazol-4-yl)benzenethiol is formed more quickly than thiadiazole ring opening occurs, making the heterocyclic ring tolerant toward the base.
Reaction of 1-(2-chloro-5-nitrophenyl)ethanone 1, via Willgerodt-Kindler routes, using the primary and secondary amines 2a-k resulted in a simple, efficient three-component one-pot synthesis of 2-aminobenzo[b]thiophenes 3a-k.
A reaction of 4-(2-mercaptophenyl)-1,2,3-thiadiazoles with an oxidant in the presence of 1.1 equiv of base afforded good yields of benzo[4,5]thieno[3,2-d][1,2,3]thiadiazoles via the intramolecular oxidative nucleophilic substitution of a hydrogen (ONHS) pathway. The reaction of 4-(2-mercaptophenyl)-1,2,3-thiadiazoles in the presence of ≥2 equiv of base gave 2-mercaptobenzo[b]thiophenes via an anionic ring-opening/ring-closure pathway.
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