Bioorthogonal Cycloadditions of C3‐Trifluoromethylated 1,2,4‐Triazines with trans‐Cyclooctenes

Abstract

Abstract1,2,4‐triazines are a valuable class of heterodienes that can be employed in inverse electron‐demand Diels–Alder reactions. However, their broader application in bioorthogonal chemistry is limited due to their low reactivity. This article focuses on 3‐(trifluoromethyl)‐1,2,4‐triazines, which can be efficiently prepared in a one‐pot reaction from NH‐1,2,3‐triazoles. These triazines are highly reactive in reactions with strained cyclooctenes, giving second‐order rate constants as high as 230 M−1 s−1. Despite their high reactivity, the compounds remain sufficiently stable under biologically relevant conditions. We show that some of the compounds are fluorogenic, a property of potential use in bioimaging. In addition, we demonstrate the successful application of the triazines in labeling model biomolecules. Our work shows that the reactivity of 1,2,4‐triazines can be enhanced by the 3‐CF3‐substitution, which we consider an important step toward the wider use of this promising class of reagents.