Keto-1,3,4-thiadiazoles

Hydrazines (of type 285 R =Me, Ph, orC6H4N02-m) are similarly converted by means of jS-keto-esters into l-(l,2,4-thiadiazol-5-yl)-3-alkylpyrazol-5-ones (286), and thence by p-nitrosodialkylanilines into the azomethine dyes (287), the absorption spectra of which have been recorded.176... 

Novel indole derivatives continue to be found in marine organisms those reported recently include dendrodoine (3), a cytotoxic thiadiazole derivative, which occurs in the tunicate Dendrodoa grossularia, from Brittany,4 and the keto-lactam (4), one of two lactams isolated from the Caribbean sponge Hali-chondria melanodocia.5... 

The 5-hydrazino-l,2,4-thiadiazoles (152) are stable in acid and base and readily form hydrazone derivatives on reaction with suitable carbonyl compounds. Thus, (152 R = Me, Ph, m-02NC6H4) reacts with /3-keto esters to form 3-alkyl-l-(l,2,4-thiadiazol-5-yl)pyrazolin-5-ones (161) which undergo coupling with p-nitrosodialkylanilines to form azomethine dyes (162) (65AHC(5)119>. 

Substituted l,3,4-thiadiazol-2-ylhydrazines (152) react with a-keto acids to give the hydrazones (153) which cyclize in acid to 1,3,4-thiadiazolotriazines (154 Scheme 15). Treatment of (152) with a-cyanoacetophenone gives the pyrazolyI[l,3,4]thiadiazole (155)... 

Azole approach. 2-Amino-l,3,4-thiadiazoles react with appropriately substituted a,/3-unsaturated carbonyl compounds to form fused pyrimidines (729). The orientation of the substituents in the fusion products suggests that the reaction is initiated by Michael addition of the amino group. 1,3-Dicarbonyl compounds will condense in the same manner to yield the salt (729) from a /3-keto ester the 5-oxo derivative (730) is formed (73ABC1197). 

Treatment of 2,5-diamino-l,3,4-thiadiazole with an a-haloketone in ethanol, followed by reaction of the resulting 2-imino-3-(a-keto-alkyl)-5-amino-l,3,4-thiadiazoline hydrohalide (33) with aqueous ammonia, and then excess of hydrazine hydrate, leads to 1 -amino-imidazole-2-thiones (34).144... 

Dimethyl-S-(l,2,3-benzotriazinyl-4-keto)methyl Phosphorodithloate 0,0-Dimethyl S-(3,4-Dihydro-4-keto-l,2,3-benzotriazinyl-3-methyl) Dithiophosphate 0,0 -Dimethyl-S-[(2-methoxy-l,3,4-thiadiazol-5(4H)-one-4-yl)methyl] Dithiophosphate 0,0-Dimethyl S-4-Oxo-l,2,3-benzotriazin-3(4H)-ylmethyl Phosphorodlthioate 0,0-Dimethyl-S-(4-oxobenzotriazin-3-methyl)-dithiophosphat... 

From Diazo-keto-amides. A classical synthesis of 1,2,3-thiadiazoIes (3) involves the cyclization of a-diazo-/3-keto-amides (2) with hydrogen sulphide and catalytic amounts of ammonia. Under similar conditions, diazo-compounds of structure [4 R = Me or Et, RR = (CHj)6l gave the hydrazones (5) rather than the desired 1,2,3-thiadiazoles (3). ... 

From Hydrazones. The synthesis of l,2,3-thiadiazole-4-carboxylic acids by the action of thionyl chloride on ethoxycarbonylhydrazones of a-keto-acids has been applied to j3-phenylpyruvic acid. The reaction produces a mixture of 5-phenyl-l,2,3-thiadiazole-4-carboxylic acid (6 X = OH), its acid chloride, and the oxadiazine (7), which is converted into (6 X = Cl) in boiling thionyl chloride. ... 

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