L–aspartic acid chelan–Cu (II) complex coted on ZrFe2O4 MNPs catalyzed one–pot annulation and cooperative geminal-vinylogous anomeric–based oxidation reactions

Abstract

In the present study, a novel chelan complex – l-aspartic acid with copper (II) – is well prepared on the surface of silica-modified nanomagnetic zirconium ferrite as a new catalytic support for high-performance catalysis applications. Regarding the CPTMS utilization as a linker, both of the carboxylate functional groups in l-aspartic acid remained unchanged and, finally, coordinated to metal sites. Moreover, the [ZrFe2O4@SiO2–n–Pr–ASP–Cu(II)] complex exhibited significant catalytic activity in the synthesis of Pyrano[2,3–c]pyrazoles and 2–amino–3–cyanopyridine derivatives under green conditions. The mechanistic studies revealed the same Knoevenagel condensation – Michael addition – cyclization sequence for both of these reactions. However, regarding 2–amino–3–cyanopyridines, a cooperative geminal-vinylogous anomeric-based oxidation occurred at the last step, leading to the aromatization of 1,4–dihydropyridine intermediates to pyridine. Notably, a wide variety of aryl and hetero-aryl aldehydes – bearing both electron-releasing and electron-withdrawing groups – were employed for the synthesis of six-membered heterocycles.