1.2.4- Triazoles 5-amino-3-mercapto- from

Several ring-closure reactions for [l,2,4]triazolo[3,4- ][l,3,4]thiadizines have been described, and all these procedures started from 3-mercapto-4-amino[l,2,4]triazole 135 (Scheme 26). A common structural feature of the reagents is the presence of the CH2X (X = halogen atom) moiety which allows the alkylation at the sulfur atom followed by a ring-closure reaction via an elimination step. Some typical ring closures are shown in Scheme 26. 

Qualitative spot tests for aldehydes, in the presence of ketones, are generally only reliable for water-soluble compounds. This problem can be overcome by the use of 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole (Purpald , Aldrich Chemical Company) in the presence of Aliquat (Scheme 5.27). Under aerial oxidation, the initially formed colourless cyclic adduct changes colour through red to purple. The colourless cyclic aminal can also be formed by ketones, but only the adducts derived from the aldehydes are oxidized to the purple bicyclic aromatic system [28]. Weakly electrophilic aldehydes, e.g., 4-methoxybenzaldehyde, reacts slowly, but will give the positive coloration upon gentle heating to ca. 70°C for one or two minutes. 

Coumarinyl-substituted thiazolo[3,2-h][l,2,4]triazoles have also been reported. They are available in one step by reaction of 5-aryl-3-mercapto[l,2, 4]triazoles with 3-bromoacetylcoumarin (ethanol, reflux, 8 h yield 44-65%) (81AP435) or in a two-step reaction from the corresponding S-alkylated intermediates with PPA [93MI2 94IJC(B)579]. 2-Aminothiazolo[3,2-h][l,2,4]triazoles are also available from 3-mercaptotriazoles. Treatment of 5-amino-3-mercaptotriazole with chloroacetone (DMF, K2CO3) and subsequent acid-catalyzed cyclization yields 146 [90JAP(K)02/142797]. 

V-Amino-3-mercapto-1,2,4-triazoles (240) add DMAD to give adducts 241 derived from initial attack by sulfur.168... 

Amino-5-mercapto-l,2,4-triazole [16691-43-3] M. 116.1, m 298 , pKeskd 3.0, pKEst(2) Recrystd from H2O and dried in vacuo. The acetyl derivative has m 325° (dec) after recrystn from H2O. [Beilstein 26, 3rd/4th SuppI p. 1351.] Also recrystd from EtOH/H20 (3 1, Ig in 50 mL, 50% recovery), m 300-302° dec subject to heating rate (Xmax 263nm, log e 4.12), and S-Benzyl derivative when crystd from CgHg/EtOH (20 1), or CHClj/EtaO has m 109-111° [Godfrey and Kruzer J Chem Soc 3437 7960]. 

Aryl-2-(carboxymethyl)(or carboxyethyl)thiazolo[3, 4 2,3]-l,2,4-triazolo[5,4-3]-l,3,3-thiadiazines 234 are obtained from 2-aryl-3-thioureido-4-thiazolidinones 235, which are formed by the addition-condensation of aldehyde thiosemi-carbazones 237 and mercaptoacetic acid. Compounds 235 undergo chemoselective intramolecular heterocyclizations to 5-aryl-2-mercapto-l,5-dihydrothiazolo[3,4- ]-l,2,4-triazoles 236, which in turn undergo condensation with a-amino acids to yield 1,3,5-thiadiazines 234 (Scheme 44) <1994JFA811>. 

Sodium hydroxide 5-Mercapto-l,2,3-triazoles from 5-amino-l,2,3-thiadiazoles... 

IR data for Co(II), Ni(II) and Cu(II) complexes of pyridine-2-(17f)-thione-3-cyano-4,6-dimethyl-5-phenylazo) and related ligands show coordination through the thioenol S and cyano N atoms." " The Co(II), Ni(II), Zn(II) and Cd(II) complexes of lH-l,2,4-triazole-3-thiol and 3-amino-5-mercapto-1,2,4-triazole have IR spectra consistent with ligand coordination through the ring N and exocyclic S atoms." Rh, Ir, Pd and Pt complexes containing mono-, di- and trisubstituted thioureas, all show IR bands from -coordinated ligands." ... 

El-Sayed AM, Khodairy A (1998) Synthesis of new fused and spiroheterocycles derived from 4-amino-5-mercapto-3-trifluoromethyl-l,2,4-triazole. Phosphoras Sulfur Silicon 132 41—52... 

Amino-3-mercapto-4H-l,2,4-triazoles from 3-aroylditbiocarbazic acids... 

Sensitization of the respiratory tract may result from dermal contact with a sensitizing chemical [30-32], Several studies have made this association for chromate [33], latex [34], the herbicide 3-amino-5-mercapto-l,2,4-triazole [35], and trimelUtic anhydride, which is a respiratory sensitizer when inhaled [36, 37],... 

Within the huge field of heterocyclic rearrangements [53], the Dimroth rearrangement gives 5-mercapto-l,2,3-triazoles from 5-amino-l,2,3-thiadiazoles and allows interconversion of 5-amino-l,2,3-triazoles into a mixture of isomers under basic condition [54]. Thus, this reaction, discovered in 1909, involves a linear intermediate that can cyclize into two isomeric compounds (Scheme 15) [55]. This ring-chain tautomerization is reversible, but the equilibrium can be pushed toward an end if one of the two isomers is stabilized. 

Synthesis of 5-Mercapto-l,2,3-Triazole Derivatives from 5-Amino-l,2,3-Thiadiazoles... 

The partial inhibition of the hydrolysis observed at pH < 4, and the negative salt effect, may be attributed to a specific cation-anion interaction. The proposed mechanism receives further support from the observed effects on the hydrolysis rates of increased viscosity of the medium and of added inorganic nucleophiles. Hydrazine or alkylhydrazines cleave and recyclize 1,3,4-thiadiazolium salts (114) to 1,2- or l,4-dihydro-l,2,4,5-tetrazines (115) in high yield. The action of arylhydrazine results in the alternative recyclization of the probable intermediate ArNHN=CR2NR N=CR SH, to 4-amino-1,2,4-triazolium salts (116). 5-Amino-2-imino-3-phenacyl-l,3,4-thiadiazolines (117) isomerize in boiling ethanol to 5-amino-3-mercapto-l-phenacyl-l,2,4-triazoles (118). This example... 

Condensed 1,3f4-Thiadiazoles. - Triazolof3,4-b][1,3,4Jthiadiazoles and thiadiazolines are prepared by cyclisation of 3-mercapto-4-amino-1,2,3-triazoles with substituted alkyl carboxylic acids or treatment with HCl followed by reflux with aldehydes. Thiazolo[4,3-b]M,3,4Ithiadiazoles (368 R=Me,Ph,H,R =Ar) result from treatment of acyl rhodanines (367) with PCl. Further reactions of the former have been reported. Imidazo [2,3-b][1,3,4]-... 

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