A New Schiff Base Complex of Aminoguanidin Established on γ-Fe2O3 for the Synthesis of Hexahydroquinolins

Hexahydroquinolines (HHQs) are the unsymmetrical derivatives of 1,4-DHPs with an improvedstructural scaffold and many pharmacological properties such as antihypertensive, antimalarial,antiasthmatic and tyrosine kinase inhibitory activities [1,2]. Generally, HHQs aresynthesized by the Hantszch condensation method, which involves a one-pot four-componentcondensation reaction of aryl aldehydes, β-ketoesters, 1,3-cyclohexanedione derivatives, andammonium acetate. Several catalysts were reported for the synthesis of HHQs. Even though,synthesis of HHQs could be proceeded by these methods, there still exist some problems relatedto the use of metal catalysts, expensive reagents, non-recoverable catalysts, difficultwork-up, high reaction temperature, long reaction times, and effluent pollution. Therefore, thedesign of a reusable heterogeneous catalyst for the synthesis of HHQs is a key aspect ofachieving the aim of sustainable chemical synthesis. In this paper, in continues of our recentworks on the introduction of new heterogeneous catalysts [3,4], we have synthesized a newSchiff base complex of aminoguanidin established on γ-Fe2O3.After its characterization bydifferent methods, we have used it as a new heterogeneous catalyst for the synthesis of HHQsby one-pot four-component condensation reaction of aryl aldehydes, β-ketoesters, 1,3-cyclohexanedione derivatives, and ammonium acetate. By this method various HHQs weresynthesized in good to high yields. The catalyst was easily isolated by an external magnet andreused five times without any loss in its catalytic activity.