Metal-Free Synthesis of Functional 1-Substituted-1,2,3-Triazoles from Ethenesulfonyl Fluoride and Organic Azides

Angew Chem Int Ed Engl. 2020 Jan 13;59(3):1181-1186. doi: 10.1002/anie.201912728. Epub 2019 Nov 28.

Abstract

The boom in growth of 1,4-disubstituted triazole products, in particular, since the early 2000's, can be largely attributed to the birth of click chemistry and the discovery of the CuI -catalyzed azide-alkyne cycloaddition (CuAAC). Yet the synthesis of relatively simple, albeit important, 1-substituted-1,2,3-triazoles has been surprisingly more challenging. Reported here is a straightforward and scalable click-inspired protocol for the synthesis of 1-substituted-1,2,3-triazoles from organic azides and the bench stable acetylene surrogate ethenesulfonyl fluoride (ESF). The new transformation tolerates a wide selection of substrates and proceeds smoothly under metal-free conditions to give the products in excellent yield. Under controlled acidic conditions, the 1-substituted-1,2,3-triazole products undergo a Michael addition reaction with a second equivalent of ESF to give the unprecedented 1-substituted triazolium sulfonyl fluoride salts.

Keywords: acetylene; click chemistry; cycloaddition; heterocycles; synthetic methods.