Cyclization of 1‐substituted‐3‐thiosemicarbazides to triazole derivatives under alkaline conditions

Abstract

Under both weakly and strongly alkaline conditions, 1‐alkyl‐2,5‐dithiobiureas (1‐alkyl‐thiocarbamoyl‐3‐thiosemicarbazides) form 4‐alkyl‐5‐amino‐1,2,4‐triazoline‐3‐thiones and 4‐alkyl‐1,2,4‐triazolidine‐3,5‐dithiones in varying proportions. 1‐Alkoxythiocarbonyl‐3‐thiosemicarbazides expel hydrogen sulfide under weakly basic conditions to form the corresponding 5‐alkoxy‐1,2,4‐triazoline‐3‐thiones. In a strongly alkaline environment, however, these alkoxy‐thiocarbonyl thiosemicarbazides eliminate alcohol to form the appropriate 1,2,4‐triazolidine‐3,5‐dithiones. 1‐Alkoxycarbonyl‐3‐thiosemicarbazides eliminate alcohol in both weakly and strongly basic media to give 5‐thiono‐1,2,4‐triazolidine‐3‐ones. Cyclization mechanisms of these thiosemicarbazides are postulated.

Thermolysis of symmetrical dithiobiurea and thioureidoethylthiourea derivatives

“…Their formation may be explained in terms of intramolecular nucleophilic attack by either the 2-thiol or the NH group and detachment of the RNH-or HS-moiety as depicted in Schemes 2 and 3. When aniline or allylamine is eliminated, the product would be a 5-substituted amino-3H- [1,3,4]thiadiazole-2-thione 9a,b, whereas It has been reported that ethylenediamine when reacting with allylisothiocyanate furnishes a linear thiourea, which in turn is cyclized to a bis-thiazoline [10]. The present work was also undertaken to discuss the intramolecular heterocyclization of 2a-c.…”

“…Alkali catalyzed thermal cyclization of 1-alkyl-and 1,6-dialkyl-2,5-dithiobiureas results in the formation of compounds 5 and 9 (R = Me, Et, and n-Pr) [6]. Under same conditions, 1-alkyl-6-aryl-2,5-dithiobiureas give thiadiazolethiones 9 and triazolidine-3,5-dithiones 5, when the alkyl groups are methyl or ethyl [4,6]. The ring-closure of 1-ethoxycarbonyl-and 1,6-bis(ethoxycarbonyl)bithiourea proceed under the influence of acids giving 5-amino (or mercapto)-2-ethoxycarbonamide-1,3,4-thiadiazoles as well as 2,5-bis(ethoxycarbonamido)-1,3,4-thiadiazole [7].…”

Chemistry and heterocyclization of dithiobiurea and thioureidoalkylthiourea

“…1,6‐Dimethyl‐2,5‐dithiobiurea 4 cyclized under either strong or weak basic conditions to produce compound 88 as the major product and in minor amount of compound 4‐methyl‐5‐methylamino‐1,2,4‐triazoline‐3‐thione 89 was also obtained (Scheme ) [95].…”

“…When 1‐alkyl‐2,5‐dithiobiureas 4 were refluxed with sodium methoxide in methanol, the reaction directly produced 4‐alkyl‐5‐amino‐1,2,4‐triazoline‐3‐thiones 89 (Scheme ) [95].…”

1,3,4-Thiadiazole, 1,3,4-thiadiazine, 1,3,6-thiadiazepane and quinoxaline derivatives from symmetrical hydrazine-1,2-dicarbothioamide as well as N, N″-ethane-1,2-diylbis(thiourea) derivatives

“…Several authors have investigated under various conditions the heterocyclization of compounds having an extended urea-like chain such as 1,4-and 2,4-disubstituted thiosemicarbazides [21][22][23], 1-substituted-3-thiosemicarbazides [24], 1-acylbithiourea [25], 1,6-disubstituted-2,5-dithiobiureas [26], 1-aryl/alkyl-2-thiobiureas [27] and thiocarbohydrazides [28]. We report herein the results of our recent investigations on the reactions of symmetrical hydrazine-1,2-dicarbothioamide as well as N,N''-ethane-1,2-diylbis(thiourea) derivatives with both chloranil (10a) and bromanil (10b).…”