5-Mercapto-1,2,4-triazolo pyrimidine

According to the systematic nomenclature these substances were first named l-f-triazolo[d] pyrimidines in compliance with the general principles of the Ring Index/ More recent papers and Chemical Abstracts indexes use the term i -triazolo[4,5-d]pyrimidine (147) in accord with the lUPAC nomenclature. The numbering of substituents when using the last-mentioned name is different from that of the 8-aza analogs. For the formulas of oxygen and sulfur derivatives names derived from the lactim or thiolactim form are almost exclusively in use (in common with the purine derivatives). These derivatives are thus described as hydroxy and mercapto derivatives, respectively. The name 1,2,3,4,6-pentaazaindene is used only rarely for this system. 

Hydrolytic fragmentation of the C5-N6 part took place upon heating 7-methyl-5-propyl-2-thioxo-l,2,4-triazolo[l,5-c]pyrimidine (129) with hydrochloric acid. 3-Acetonyl-5-mercapto-l,2,4-triazole (130) and butanoic acid were obtained as a result of N4-C5, C5-N6, and N6-C7 bond cleavages (65JCS3369) (Scheme 50). 

Oxidation of 2-mercapto-l,2,4-triazolo[l,5-c]pyrimidines (174) with chlorine or bromine in water (64BRP951652 65JCS3369), with hydrogen peroxide and chlorine (95MIP1), as well as with sodium chlorate in hydrochloric acid (94JMC2371) gave the corresponding 2-sulfonyl halide derivatives 175. Oxidation of the 2-alkylmercapto compounds 176 to the 2-alkylsufonyl derivatives 177 was made with ammonium peroxodisulfate and sulfuric acid... 

Heating 5-hydroxy-3-mercapto-7-phenyl-1,2,4-triazolo[4,3-a]pyrimidine (145) with aniline gave the 2-anilino-4-hydroxy-6-methylpyrimidine (144)... 

A number of 5- and 7-monosubstituted and 5,7-disubstituted [l,2,4]triazolo[l,5-a]pyrimidines have resulted from reactions on the 5,7-dihydroxy, -aminohydroxy and -hydroxymercapto derivatives. The hydroxy derivatives were amenable to chlorination which was followed by a variety of nucleophilic substitution reactions or hydrogenolyses. The mercapto groups were susceptible to alkylation and subsequent nucleophilic substitution (61CPB801,63CPB845). 

Phenacyl bromides react (86JHC43) with anhydro l-amino-5-aryI-2-mercapto-l,2,4-triazolo[3,2-c]quinazolin-4-ium hydroxides (53) through pyrimidine ring-opening and simultaneous formation of the 1,3,4-thiadiazine nucleus to give 54. Compound 514 was also obtained [86JAP(K)61260085] when 2-hydrazino-5-methyl-6/f-l,3,4-thiadiazine (513) was cyclized with aryloxyacetyl chlorides. 

Shirakawa, K. 1-Mercapto-s-triazolo[3.4-b]pyrimidine, (Takeda Pharma-... 

When 7-hydroxy-l,2,3-triazolo[4,5-d]pyrimidine (25) and its 3-benzyl derivative were thiated by phosphorus pentasulfide, they gave 7-amino (and benzylamino)thiazolopyrimidine (26), respectively, instead of the expected 7-mercapto isomer 27 [67JCS(C)1856], The thermal rearrangement of the benzylated isomer reaches an equilibrium point which favors the thiazolo isomer. The rates for such equilibration in a series of analogs of 7-mercapto-... 

Treatment of the 3-amino- or 3-mercapto-l,2,4-triazolo[4,3-c]pyrim-idines 80 with aqueous hydrochloric acid at reflux caused further fragmentation of the pyrimidine ring to give the 3-acetonyl-5-amino- or 5-mercapto-1,2,4-triazoles 81 in addition to the corresponding alkanoic acid (63JCS5642 65JCS3369) (Scheme 35). 

S-Alkylation of 2-mercapto-l,2,4-triazolo[4,3-c]pyrimidine (94) [94JCR (S)412 95MIP1] or their sodium salts (79AJC2713) gave the corresponding 2-alkylmercapto derivatives 95 (Scheme 41). 

Hydroxy-4-mercapto-6-phenylpyrimidine refluxed 2 hrs. with 98%-hydrazine hydrate -> 2-hydroxy-4-hydrazino-6-phenylpyrimidine (Y ca. 90%) refluxed 3 hrs. with 98%-formic acid 5-hydroxy-7-phenyl-s-triazolo[4,3-c]pyrimidine... 

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