Acemannan from Aloe vera Extract: A Catalyst-Free, Approach for the Access of Imidazole-Fused Nitrogen-Bridgehead Heterocycles

Abstract

Abstract: A series of 2-phenyl substituted imidazo-pyridines, pyrazines and pyrimidines were synthesized through an efficient one-pot, environmentally benign, and regioselective strategy which involves the reaction between 2-bromocarbonyl compounds and 2-aminopyridines, 2-aminopyrazines, 2- aminopyrimidines, respectively using aloe vera/water (3:2) as a green promoting media. To the best of our knowledge, this is the first aloe vera promoted protocol for the synthesis of this important scaffold having potential applications in medicinal and materials chemistry. The use of aloe vera as a biorenewable and biodegradable reaction medium-cum-promoter, operational simplicity, use of readily available substrates, mild reaction conditions, broad substrate scope, short reaction time, easy workup, and high yields, makes the disclosed protocol a superior alternative to existing methods. Substituted imidazo-pyridines, pyrazines and pyrimidines were obtained with 95%, 76% and 84% yields, respectively.