Sustainable sonochemical synthesis of N‐protected piperazine‐propargylamines using ionic liquids and CuI

We present a simple method to prepare diverse benzimidazolium and imidazolium ionic liquids (ILs) from common starting materials imidazole and benzimidazole. These green ILs promote the synthesis of N ‐substituted piperazinyl propargylamines via a versatile CuI‐catalyzed coupling of aldehydes, secondary amines, and alkynes under ultrasound. Remarkably, the method works across a broad range of substrates, including diversely substituted aldehydes, heterocycles, cyclic amines, and phenylacetylenes. To understand this versatility, we investigated the influence of IL structure ( N ‐substitution, anion) on reactivity. Symmetrical long‐chain substituents on the benzimidazolium cation and bromide (Br − ) anions led to the most efficient propargylamine formation. This approach offers a sustainable and efficient route to propargylamines with minimal waste and catalyst/IL recyclability over five cycles.