1,2,3-Triazoles, l-amino

Tandem azidination- and hydroazidination-Hiiisgen [3 +2] cycloadditions of ynamides are regioselective and chemoselective, leading to the synthesis of chiral amide-substituted 1,2,3-triazoles <06OBC2679>. A series of diversely l-substituted-4-amino-l,2,3-triazoles 132 were synthesized by the copper-catalyzed [3+2] cycloaddition between azides 130 and ynamides 131 <06T3837>. 

A similar route to the i -triazolo[4,5-d]pyrimidine ( 8-azapurine ) ring system has been developed. This involves reaction of 4-amino-l,2,3-triazole-5-carboxamide or its ring iV-alkyl derivatives with formamide (Scheme 46). - 232-234 pyrimidone derivatives thus... 

Albert. A., 4-Amino-l,2,3-triazoles, 40, 129 The Chemistry of 8-Azopurines (1,2,3-Triazolo[4,5-d]pyrimidines), 39, 117 Annelation of a Pyrimidine Ring to an Existing Ring, 32, 1 Covalent Hydration in Nitrogen Heterocycles, 20, 117. 

Similarly, 1,3 -dipolar cycloadditions of benzenesulfonyl azides to N,N- diethylaminoprop-1-yne led to 1,2,3-triazoles (72a) and a-diazoamidines (72b). With the aid of IR and H NMR data these were shown to exist in a tautomeric equilibrium (70JOC3444). With IR and H NMR data a 5-aminotriazole-diazoamidine equilibrium (73a) s (73b) was established (70TL2823, 72CB2963, 72CB2975). However, 4-amino-l,2,3-triazole (74a) proved to be stable and no ring-chain tautomerism could be identified (73TL1137). 

TL2823, 72CB2963, 72CB2975). However, 4-amino-l,2,3-triazole (74a) proved to be stable and no ring-chain tautomerism could be identified (73TLH37). 

The hydrolysis of an 8-azapuiinone usually was more difficult. Thus, 8-azapurin-6-one (31) required heating (with 2 IVhydrochloric acid, 90 C, 2 h) for hydrolysis to 4-amino-l,2,3-triazole-5-carboxamide (32). Further stabilization of the pyrimidine ring, as in 2-amino-8-azapurin-6-one, shifted the site of fission to the triazole ring, and consequently more severe conditions were required (6IV HQ, 150 C, 2 h). The product was 2,4,5-triamino-pyrimidin-6-one. ... 

Amino-8-azapurine 1-oxide, stirred with 10 hydrochloric acid (room temp, 5 min) gave 4-amino-l,2,3-triazole-6-carboxamidoxime in 81% yield. 

The synthesis from triazoles that, in spite of the poor yield (19%), most shaped future practice was that of Yamada who, by heating 4-amino-l,2,3-triazole-5-carboxamide (73a) with urea (165°C, 5 h), obtained 8-aza-purine-2,6-dione (74) plus the intermediate 4-ureido-l,2,3-triazole-5-car-boxamide. 

Various uses have been suggested for 4-amino-l,2,3-triazoles, and many patents have been issued. However, no major commercial products, based on this structure, have yet appeared. 

The 4-amino-l,2-3-triazoles are much used, as easily accessible starting materials, for preparing more complex heterocycles. This section will deal first with examples where the 4 and 5 positions of the triazole participate in forming the new ring. 

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