A novel and facile synthesis of mesoionic 1,2,4-triazolium-3-thiolate derivatives

Formation of thiadiazole, thiadiazine, thiadiazepine and pyrazole derivatives in the reaction of 2,4-disubstituted thiosemicarbazides with tetracyanoethylene

“…In principle, one can discuss initial tricyanovinylation products 20 and 22 originating from the primary adducts 19 and 21 from thiosemicarbazide 7 and TCNE 2 (Scheme 4) since products 11 may also be formed from 20 with loss of malononitrile, and adducts of 2 to N-4 of 1,4-disubstituted thiosemicarbazides have been discussed before. 21 Scheme 4. Conceivable alternative adducts from the reaction of thiosemicarbazides 7a-e with TCNE 2.…”

“…Upon mixing N-substituted-2-phenylhydrazinecarbothiamides 3a-c with TCNE 2 mesoionic 1,2,4-triazolium-3-thiolate derivatives 4a-c were observed (Scheme 1). 21 The reaction of 2-substituted hydrazinecarbothioamides 5a-e with TCNE 2 afforded 2{amino-[5-amino-2-(substituted diazenyl)thiazolyl]methylene}malonitrile 6a-e (Scheme 1). 22 This unique and variable reactivity shown in the three aforementioned examples warranted a more detailed investigation.…”

An Update of the Use of Thiocarbohydrazides and Thiosemicarbazides in the Preparation of Heterocycles and Their Biological Importance

“…Treatment of N ‐substituted‐phenylhydrazinocarbothioamides with TCNE ( 88 ) in dry EtOAc, with admission of air at r.t producing mesoionic 1,2,4‐triazolium‐3‐thiolate derivatives 139a – c in 67–76% yields (Scheme ) .…”

Eschenmoser‐Coupling Reaction Furnishes Diazenyl‐1,2,4‐triazole‐5(4H)‐thione Derivatives

“…Mesoionic 1,2,4‐triazolium‐3‐thiolate derivatives have been synthesized during the reaction of N ‐substituted 2‐phenylhydrazinecarbothioamides with tetracyanoethylene (TCNE) via nucleophilic attack of R N 4 H on C=C with elimination HCN, followed by cyclization …”