Synergistic catalysis of bifunctional polyacrylonitrile fiber for the synthesis of (E)-α,β-unsaturated esters from aldehydes by decarboxylative Doebner–Knoevenagel reaction

Abstract

A series of monofunctional and bifunctional polyacrylonitrile fiber catalysts have been successfully prepared to catalyze the decarboxylative Doebner–Knoevenagel reaction of aldehydes and monoethyl malonate for the syntheses of the (E)-α,β-unsaturated esters. Among which, the catalyst PANPDFII/I shows the best synergistic catalytic activity with high yields (89–96%), stereoselectivities (Z:E>99:1) and reusability (up to 8 times). The influences of the N position on aminopyridine moiety, solvent and temperature on the catalytic system were investigated in detail. This catalytic system can process well in higher or lower polar organic solvents instead of moderate polar solvents, which is an interesting phenomenon in organic catalysis, and the reasons are explained in this work. Furthermore, a DMAP (4-dimethylaminopyridine) and piperazine synergistic catalytic mechanism in the micro-environment of the fiber catalyst has been conceived to explain the high catalytic performance of this catalytic system. Besides, the fiber catalyst PANPDFII/I shows high application potential in industry for its good performance in scaled-up experiment, as well as its advantages of the easy preparation, high mechanical strength, flexibility and high stability in air.