1.2.5- Thiadiazolin-3-ones, synthesis

A useful method for the synthesis of 5-chloro-l,2,4-thiadiazoles (206) is the reaction of amidines with trichloromethylsulfenyl chloride (see Equation (30)). 3-Halo derivatives (349) (X = Cl, Br, I) (Equation (57)) have been obtained in moderate yields from the corresponding amines (348) via the Sandmeyer-Gatterman reaction <84CHEC-I(6)463>. 3-Chloro-l,2,4-thiadiazolin-5-ones (350) and (351) can be prepared by reacting chlorocarbonylsulfenyl chloride with carbodiimides or cyanamides respectively (Scheme 79) <84CHEC-I(6)463>. 

A one-step procedure for the synthesis of 5-arylimino-l,2,4-thiadiazolin-3-ones (273) from a mixture of alkyl azide, substituted phenyl isothiocyanate and aryl or alkyl isocyanate has been reported (76AG(E)489). Evidence was presented to support the proposal that a... 

One of the most commonly used methods to obtain 2-amino-l, 3,4-thiadiazolines is the heterocyclization of thiosemicarbazides. An efficient one-pot synthesis of 2-amino-l,3,4-thiadiazoles 125 features the in situ formation of thiosemicarbazides 123 by the reaction of carboxylic acid hydrazides 121 with trimethylsilyl isothiocyanate (TMSNCS) 122, followed by cyclodehydration of thiosemicarbazides 123 under acidic conditions (13RSC6813). 

Type D Syntheses [C—N—C—S—N], The synthesis of A -l,2,4-thiadiazolines from potassium methyl cyanoiminodithiocarbonate, MeS C(=NCN)SK, and A -chloro-amidines (see Vol. 3, p. 682) has been extended by the inclusion of other A -chloro-cyanamide derivatives, e.g. NH2C(=NCl)OR, as one of the reactants. In this case, condensation at 5 °C produces 2-alkoxyimidoyl-3-imino-5-methylthio-A -l,2,4-thiadiazolines in 41—79% yield. They are dealkylated to the amides by methanolic hydrogen chloride and readily undergo aminolysis to the amidines, iV-Chloro-guanidines and A -chloroguanylurethane may be used similarly in this general synthesis. ... 

Other Syntheses. 3,5-Diaryl-l,3,4-thiadiazoline salts (139) are accessible by the cyclization of the appropriate substituted l-phenyl-2-thiobenzoyl-hydrazines by triethyl orthoformate in ether saturated with hydrogen chloride, The condensation of phenacyl thiocyanates ArCOCHaSCN, with diazotized arylamines provides a convenient one-step synthesis of 4-aryI-2-benzoyl-5-imino-A -l,3,4-thiadiazolines (141). Their alternative synthesis from (140) and potassium thiocyanate confirms the assigned structure. ... 

Type E Syntheses [CNCS + N].— The interaction of thiobenzoyl isocyanate and nitrosobenzene yields, surprisingly, the l,2,4-thiadiazolin-3-ones (79) (58%), with elimination of oxygen, the fate of which is as yet not elucidated. The formulation of the products is confirmed by their unequivocal synthesis by the oxidative cyclization of (80). ... 

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