Direct Routes to Thiazolotriazoles by Cyclization

Visible-light-mediated regioselective synthesis of novel thiazolo[3,2-b][1,2,4]triazoles: advantageous synthetic application of aqueous conditions

From a green chemistry perspective, sustainable irradiation as the power source and water as the solvent have certainly grabbed the attention of chemists in recent times because their use helps reduce the hazardous ecological footprints of organic synthesis. In the present work, we have established an efficient, straightforward and green protocol for the regioselective synthesis of novel functionalized thiazolo[3,2-b][1,2,4]triazoles. The visible-light-mediated catalyst-free reaction of diversely substituted α-bromodiketones, generated in situ by the reaction of NBS and 1,3-diketones, with 3-mercapto[1,2,4]triazoles under aqueous conditions afforded thiazolo[3,2-b][1,2,4]triazole derivatives in excellent yields. The structure of the regioisomer has been confirmed explicitly by heteronuclear 2D-NMR [(¹H-¹³C) HMBC, (¹H-¹³C) HMQC] spectroscopic and X-ray crystallographic studies. Radical initiating and trapping experiments supported the free radical mechanism for the cyclization.

One-Pot Synthesis of Some New s-Triazole Derivatives and Their Potential Application for Water Decontamination

A rapid, efficient, and one-pot protocol has been developed for the synthesis of cyclized 2,6-dimethyl-5-substituted-thiazolo[3,2-b]-s-triazoles (3a-c) through the interaction of 5-methyl-1H-s-triazole-3-thiol (1) with aliphatic ketones (2a-d) in refluxing acetic acid in the presence of a catalytic amount of sulfuric acid (AcOH/H+) while with aromatic ketones (5a-d), a mixture of uncyclized 3-methyl-s-triazolylthioacetophenone derivatives (6a-d) and cyclized 6-aryl-2-methyl-thiazolo[3,2-b]-s-triazoles (7a-d) has been produced. With this catalytic system, inexpensive sulfuric acid was utilized as a catalyst, which prevented the production of poisonous and irritating halo carbonyl compounds. On the other hand, the interaction of s-triazole 1 with cyano compounds (9a,b) afforded the corresponding 6-amino-2-methyl-5-substituted-thiazolo[3,2-b]-s-triazoles (10a,b). Similarly, treatment of 4-amino-3-methyl-s-triazole-5-thiol (12) with aliphatic and aromatic ketones (2c and 5a-e) afforded directly 3-methyl-7H-s-triazolo[3,4-b]-1,3,4-thiadiazines (13a and 14a-e). Further, reaction of 12 with cyano compounds (9a,b) under the same reaction conditions yielded the corresponding 3-methyl-s-triazolo[3,4-b]-1,3,4-thiadiazole derivatives (15a,b). The reaction mechanism was studied, and the structures of all novel compounds were verified using spectroscopy and elemental analysis. Moreover, the potential application of the synthesized compounds toward heavy metal ions and inorganic anion removal from aqueous solution has been investigated. The removal effectiveness for metal ions reached up to 76.29%, while for inorganic anions it reached up to 100%, indicating that such synthesized compounds are promising adsorbents for water remediation.