Triflic acid catalyzed intermolecular hydroamination of alkenes with Fmoc-NH2 as the amine source

Abstract

Intermolecular hydroamination of alkenes is recognized as one of the most challenging synthetic pathways for directly obtaining primary amine derivatives from alkenes. While metal-catalyzed hydroamination is well established, metal-free hydroamination for synthesizing primary amines remains an attractive yet infrequent approach. In this study, we report the hydroamination of vinyl arenes using triflic acid as the catalyst and Fmoc-NH₂ as the amine source. The optimized conditions proved effective for a range of vinyl arenes and some endocyclic alkenes, yielding moderate to excellent results (40–91%). Mechanistic investigations conducted through NMR, variable temperature NMR, kinetic studies, and control reactions indicated that the transient interaction between triflic acid and Fmoc-NH₂ inhibited styrene polymerization. Primary amines were obtained by deprotecting the Fmoc group using KOH/MeOH.