Thiadiazol-4-ones

4-Thiadiazol-2-ones (Anhydro-2-hydroxy-l,3,4-thiadiazolium Hydroxides) (243) 

The meso-ionic l,3,4-thiadiazol-2-ones (243) have been prepared from. /V-thioacylhydrazines (232) or their hydrochlorides102,103 by reaction with carbonyl chloride102 103,110 111 133,136 or methyl chloro- 

Grashey and M. Baumann, Angew. Chem., Int. Ed. Engl. 8, 133 (1969). 

Photolysis (2537 A) in methyl cyanide solution of the compound 243, R1 = Me, R2 = Ph, gives A-methylthiobenzamide.157 This reaction has been interpreted in terms of the homolysis of the valence tautomer 244, which has been detected spectroscopically (vma, 2260 cm-1 N=C=0).22 The l,3,4-thiadiazol-2-ones have dipole moments (243, R1 = R2 = Ph,/u = 7.75 D 243, R1 = Me, R2 = Ph, ft = 7.7 D) consistent with their meso-ionic formulation.113 They react with triethyloxonium tetra-fluoroborate, yielding the salts 245.6fi The compound 243, R1 = Me, R2 = Ph, and aniline gives the semicarbazide 246.135 

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In the presence of triethylamine, the reaction of 2-amino-5-methyl[l,3,4]thiadiazole 134 with 2-benzyl-5-chloro-[l,2,4]thiadiazol-2-one 135 gives 3-(benzylcarbamoylimino)-6-methyl-3//-[l,3,4]thiadiazolo[2,3-c][l,2,4]thiadiazole 138. Presumably, the first-formed intermediate 136 rearranges through the thiapentalene intermediate 137 to the fused thiadiazole product 138 (Scheme 10) <1994T7019>. 

Ph, R = NHj, with phosgene gives a novel bicyclic heterocyclic system which can be represented as a bicyclic meso-ionic l,3,4-thiadiazol-2-one (493) (Section VII,H,1). A similar reaction using A -benzoyl isocyanide dichloride (PhCO.N=(i Cl2) gives the novel meso-ionic 1,3,4-thiadiazol-2-imine (494) (Section VII,H,2). ... 

The first study has shown that dehydrodithizone (413, R = R = Ph) reacts with pentacarbonyliron to give the l,3,4-thiadiazol-2-one (509). 

Chlorocarbonylsulfenyl chloride (291) also condenses with a variety of ureas, thioureas, guanidines, carbodiimides and cyanamides to produce l,2,4-thiadiazol-2-one derivatives of types (298), (297) and (299) as indicated in Scheme 106 (70AG(E)54, 73CB3391). 

Aminothiazoles, for example, react with 179 in tetrahydrofuran to give tars, from which 2H-thiazolo[3,2-b]-l,2,4-thiadiazol-2-one (181) is isolable in 3% yield the alternative use of 180 raises the yield to 25%.161,162 The... 

Trifluoromethyl-l,3,4-thiadiazol-2-one, with a butyl bromide side chain at N-3, undergoes a ring transformation with secondary amines to give 1,3.4-thiadiazocines (56) <83HCA2714>. The reaction is thought to occur via addition of the amine to the carbonyl of the thiadiazol-2-one, as outlined in Scheme 35. A second product in the reaction is the 3-aminobutyl-thiadiazol-2-one resulting from direct nucleophilic displacement of the bromine with the amine. 

Hydrogen sulfide l,3,4-Thiadiazol-2-one azines from 2,2 -azo-l,3,4-thiadiazoles... 

HgS passed into a hot soln. of 5,5 -bis(benzylmercapto)-2,2 -azo-l,3,4-thiadiazole in dioxane-water until only a slight yellow color remains 5-benzylmercapto-l,3,4-thiadiazol-2-one azine. Y ca. 100%. F. e. s. N. Petri and O. Glemser, B. 94, 553 (1961). 

Thiazolo-[2,3-c]- and -[3,2-6]-[l,2,4]thiadiazoles [CaNgS-CaNS].—Condensations of a-amino-N-heterocycles with chlorocarbonylsulphenyl chloride in the presence of an organic tertiary base can give rise either to a 2,3- or to a 3,4-fused [1,2,4]-thiadiazolone. Thus, 2-aminothiazole yields 2JT-thiazolo[3,2-b][l,2,4]thiadiazol-2-one in THF (see Vol. 3, p. 684). The isomeric 2,3-fused system is formed in ethanol-free chloroform. 2-Amino-A -thiazoline similarly yields 5,6-dihydro-thiazolo[2,3-c][l,2,4]thiadiazol-3-one, the structure of which has been confirmed by X-TQ.y analysis. ... 

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