An Overview of 4‐ and 5‐Halo‐1,2,3‐triazoles from Cycloaddition Reactions

• Published in: European journal of organic chemistry 2021-05, Vol.2021 (18), p.2665-2679
• Main Authors: Arenas, José Laxio, Crousse, Benoît
• Format: Article
• Language: English
• Subjects: 4-Halo-1,2,3-triazoles; 5-Halo-1,2,3-triazoles; Bromine; Chemical Sciences; Chlorine; Cycloaddition; Halogenation; Halogens; Iodine; Organic chemistry; Synthesis; Triazoles
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.202100327

1,2,3‐triazoles are important scaffolds in several fields, and there is still a demand to construct these compounds, most notably the disubstituted 4, 5 compounds. The latter are obtained in different ways, but the 4‐ and 5‐halo triazoles are generally the key intermediates in their synthesis. These halogenated compounds are an extraordinary platform leading to a great chemical diversity around the 4 and 5 positions. However, their own pathways are generally put aside at the expense of the substituted triazoles. This review is focused on the main synthesis of 5‐ and 4‐halo 1,2,3‐triazoles from cycloaddition followed or not by halogenation reaction. Unlike the halogens (iodine, bromine, and chlorine), the 5‐ and 4‐fluoro 1,2,3‐triazoles will be presented separately due to their relatively more difficult and still recently challenging synthesis. This minireview reported the synthesis of the 5 and 4‐halo‐1,2,3‐triazoles which are very important key intermediates to the synthesis of 4, 5‐disustituted‐1,2,3‐triazoles. The major derivatives are the iodo‐triazoles followed by the bromide and chloride triazoles. The fluoro‐triazoles appeared more recently and are prepared by different methods.