1.2.3- triazoles formation

On heating, phenyl azide decomposes partially to give nonvolatile products which form colors with diazonium compounds. To minimize the presence of these impurities, the quantity of phenyl azide is limited to 2 drops in the triazole formation step. 

Complete removal of excess phenyl azide after triazole formation is necessary to ensure reproducible results. 

With malonic esters and amides substituted at the central carbon, triazole formation is accompanied by decarboxylation and 4-alkyl-or 4-aryl-5-hydroxytriazoles are isolated. ... 

Since the discovery of triazole formation from phenyl azide and dimethyl acetylenedicarboxylate in 1893, synthetic applications of azides as 1,3-dipoles for the construction of heterocychc frameworks and core structures of natural products have progressed steadily. As the 1,3-dipolar cycloaddition of azides was comprehensively reviewed in the 1984 edition of this book (2), in this chapter we recount developments of 1,3-dipolar cycloaddition reactions of azides from 1984 to 2000, with an emphasis on the synthesis of not only heterocycles but also complex natural products, intermediates, and analogues. 

Triazine formation, 377, 282 ac3ti cyanide, 283 semicarbazone, 282 Triazole formation... 

An interesting case of triazole formation under the influence of base is that of the bistriazoline in Scheme 58, which expels a molecule of diethylamine and yields two molecules of 1 -p-bromophenyltriazole.238 l-Vinyl-5-aminotriazolines are readily deaminated to the corresponding triazoles when eluted through a silica-gel column.222... 

The thermolysis of l-/ -ethoxyethyl-5-alkoxytriazolines at 170°C proceeds in two directions (Scheme 126) although triazole formation predominates, loss of nitrogen becomes increasingly important as the length of the 5-alkoxy chain increases.406... 

The triazoline diazo compound equilibrium may be considered to play a role in the cis-trans isomerization332 and oxidation (Scheme 119)284 of certain triazolines. Triazole formation by elimination of amine214 or alcohol405 is also postulated to involve intermediate diazo compounds (Scheme 123). Unlike normal triazolines, the inability of 1-fluorotriazolines to undergo thermolysis or photolysis reactions to yield aziridines is ascribed to the fact that the triazoline always exists in equilibrium with the diazo compound (Scheme 98).356 Spontaneous isomerizations of triazolines not... 

Examples of aromatic amines that can be dia-zotized are shown in Fig. 13.83. This extremely abbreviated list is designed to show that a wide variety of amines can be used, including hydrophobic, weakly basic, hydrophilic, and heterocyclic compounds. orf/zo-Diamines are not typically used because of their propensity to undergo triazole formation (Fig. 13.84). 

Fig. 13.83. Representative aromatic amines used Fig. 13.84. Triazole formation from the diazotiza-in azo dye synthesis. tion of an ortho-diamine.

Katritzky AR, Zhang Y, Yuming S, Sandeep K (2003) 1,2,3-triazole formation under mild conditions via 1,3-dipolar cycloaddition of acetylenes with azides. Heterocycles 60 1225-1239... 

A review on the 1,2,3-triazole formation via 1,3-dipolar cycloaddition of acetylenes with azides under mild conditions has been published <03H(60)1225>. The synthesis of a benzotriazole azo dye phosphoramidite and the subsequent use in solid phase synthesis of oligonucleotides has been reported <03TL1339>. The chemical reactivity of [l,2,3]triazolo[l,5-a]- and [l,5-c]-pyrimidinium salts has been published <03T4297>. A review on the use of benzotriazole as an ideal synthetic auxiliary has been disclosed <03CEJ4586>. 

Many of the different cycloadditions of azides to triple bonds have been reviewed extensively (socRV(46)i, b-61mi41ioo, b-71mi4iio4, 74AHC(16)33, 80HC(39)i). Some representative examples of triazole formation by cycloaddition of azides to triple bonds are given in Table 20. 

With malonic esters and amides substituted at the central carbon atom, triazole formation is accompanied by decarboxylation and 4-alkyl- or 4-aryl-5-hydroxytriazoles are isolated (69ACS(B)i09i). The 4-methoxybenzyl group has recently been found to be a versatile W-protecting group for the synthesis of AT-substituted 1,2,3-triazoles (82jcs(pi)627). 

Methods of this type are best considered as reactions of the fused ring-systems in question (see Chapter 4.15). The example illustrated in Scheme 91 is of potential interest in pharmacology (75T1363, cf. 74CPB1938). The conversion of the 1-aminoadenosine (192) into the imidazolyltriazole (193) amounts to triazole formation from an amidrazone intermediate and a formyl group derived from the pyrimidine moiety. 

Triple bonds add azides to give 1,2,3-triazoles (from carbon-carbon triple bonds) and tetrazoles (from nitriles or isonitriles). The reactions are of very wide scope, but there are few examples involving acyl azides. The formation of triazoles from acetylenes and azides in general has been reviewedand the scope of these reactions has been expanded by more recent work, a few examples of which are found in the references 255-25s triazole formation from acetylenes... 

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