Scalable, Chromatography‐Free Synthesis of 2‐(3‐Bromophenyl)‐2H‐1,2,3‐triazole through N−N Bond Forming Cyclization

Abstract

Abstract2‐(3‐Bromophenyl)‐2H‐1,2,3‐triazole is a low molecular‐weight building block that is not readily accessible in pure form by standard synthetic approaches due to competing formation of the triazol‐1‐yl regioisomer. After investigation of a wide range of synthetic routes, a process based on construction of the triazole heterocycle by cyclization of an activated dihydrazone was developed. A suitable isolation method had to be identified before embarking on a demonstration run on >100 g scale without the need for chromatography. The new process delivered the desired building block in 48 % overall yield over four telescoped steps with excellent purity (99 % a/a).