Brønsted Acidic Ionic Liquid‐Catalyzed Regioselective Synthesis of Pyrazolopyrimidines and Their Photophysical Properties

Abstract

Abstract A convenient and straightforward regioselective synthesis of pi‐conjugated pyrazolo[1, 5‐ a ]pyrimidines has been achieved via Brønsted acidic ionic liquid catalyzed tandem cyclization between 3‐aminopyrazole and chalcone derivatives in high yields. Task specific ionic liquid [1‐methyl‐3‐(4‐sulfobutyl)imidazolium‐4‐methylbenzenesulfonate] is found to be an effective catalyst for the cyclization, and the presence of both C2‐H of imidazolium moiety and acidic proton drastically enhance the catalytic activity. Substituted aminopyrazoles reacted with a wide range of functionalized α,β ‐unsaturated ketones to variety of pyrazolo[1, 5‐ a ]pyrimidine derivatives. The present protocol offers a broad substrates scope, use of non‐hazardous reagent, metal‐free environmentally benign conditions and catalyst recyclability. Comparative photophysical studies have shown high quantum yields for certain derivatives.