Substitution of the 1,2,4-Triazole

Triazole undergoes halogenation, and bromination of the triazole provides the 4,5-dibromo derivative. The 4,5-dibromotriazole was prepared by bromination of triazole with NBS. Triazoles are readily alkylated on nitrogen by alkylhalides, dimethylsulfate, diazomethane, and conjugate addition. In addition, triazoles are acylated by acyl halides and anhydrides and the alkylations are not regioselective.  

The selective formation of N-2 substituted traizoles has been recently reported. The alkylation of 4,5-dibromotriazole with ethylbromide produces the N-2 alkylated product in an 87 13 ratioThe dibromo-triazole is then readily converted into the monobromo-triazole. 

Recently propargyl alcohols were reported to undergo FeCb-catalyzed triazole propargylation to yield propargylated triazoles. A mixture of N-2 and N-1 isomers is generally produced. The products of the reaction were then further derivatized via click chemistry to synthesize bis-triazole systems. 

Biaryl-1,2,3-triazoles have been reported to undergo direct palladium-catalyzed arylation to yield annulated phenanthrenes.  

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