5-amino-3,4-dihydro-2h-1,2,4-triazole-3-thiones. synthesis and chemosensor properties

Abstract

Keywords: 4-arylalkyl-and 4-arylthiosemicarbazides, aroyl and hetaroyl isothiocyanates, 1,2,4-triazole-3-thiones, fluorescent chemosensors.Derivatives of 1,2,4-triazole have found common use in medicine [1-3] and as efficient corrosion inhibitors [4], catalysts [5], ligands [6], and chemosensors [7], Various pathways and methods exist for the synthesis and modification of both 1,2,4-triazole [8-10] and its 3-thio derivatives [11][12][13]. Greatest interest is found for one-and two-step methods for the preparation of similar structures. Hydrazides of acids and 4-substituted thiosemicarbazides in combination with isothiocyanates or cyanamides are often used for the synthesis of 1,2,4-triazole-3-thiones as the starting compounds.In previous work [14], we have shown the feasibility of using thioureas containing a 9-anthrylmethyl fragment as highly efficient chemosensors for the Hg 2+ cation. In a search for new, highly efficient sulfur-containing anion and cation sensors, 4-(9-anthrylmethyl)thiosemicarbazide (1a) was obtained starting from 9-aminomethylanthracene according to Kazakov and Postovskii [15]. In order to increase the number of coordination sites, we carried out the reaction of compound 1a with p-chlorobenzoyl isothiocyanate (2a) obtained in situ from p-chlorobenzoyl chloride and ammonium thiocyanate in acetonitrile. However, 1,2,4-triazole-3-thione (4a) was obtained as the major product instead of the expected substituted 1,2-bis(thiocarbamoyl)hydrazine 3a. This result can probably be attributed to the thermal cyclization of initially formed compound 3a upon its recrystallization from 1-butanol. Cyclic products 4b-h were also obtained in the reaction of 4-arylalkyl-and 4-arylthiosemicarbazides 1b-d with aroyl and hetaroyl isothiocyanates 2b-f (see Scheme).

Isothiocyanates: happy-go-lucky reagents in organic synthesis

“…This sulfur radical A then undergoes intramolecular radical trapping by the hydrazonic double bond and gives B. Following this, the hydrogen atom transfer from B to DDQH releases the final product 2-amino-1,3,4-thiadiazoles (85) and hydroquinone DDQH 2 . Meanwhile, DDQ gets regenerated via anodic oxidative dehydrogenation, and subsequently, cathodic reduction of proton leads to the generation of H 2 (Scheme 36).…”

“…Organic & Biomolecular Chemistry . 85 Dethe group reported a transition metal-free and base-catalyzed intramolecular hydroamination protocol for the synthesis of substituted imidazole-2-thione and spiro-cyclic imidazolidine-2-thione. Herein, propargylamine (190) participated in the reaction via initial formation of propargyl(thio)urea by reacting with isothiocyanate (189) at ambient temperature.…”

“…The initial reaction of 4-arylalkyl- and 4-arylthiosemicarbazides ( 187 ) with aroyl isothiocyanates ( 186 ) gives the substituted 1,2-bis(thiocarbamoyl)hydrazines, which are readily cyclized to 4-aroyl 5-arylalkyl- and 4-aroyl-5-arylamino-2 H -1,2,4-triazole-3-thiones ( 188 ), respectively (Scheme 79). 85…”