Malononitrile-Catalyzed and Highly Selective Method for the Synthesis of 2-((E)-1,3-Diarylallylidene)malononitriles in Ionic Liquid

Abstract

The green and highly selective reactions of aromatic aldehydes, malononitrile, and 2-(1-arylethylidene)malononitriles in ionic liquid of [bmim⁺]Br⁻ at 50°C unexpectedly gave 2-((E)-1,3-diarylallylidene)malononitriles. The modification of the reaction used 10 mol% malononitrile as catalyst at 90°C in [bmim⁺][]. A possible reaction mechanism for the formation of the product was proposed based on further experimental results. 2-((E)-1,3-Diarylallylidene)malononitriles were not detected at all in the designed reaction of aromatic aldehyde and 2-(1-arylethylidene)malononitriles at the same reaction conditions.

Keywords:

• 2-(1-Arylethylidene)malononitrile
• 1,3-diarylallylidenemalononitrile
• ionic liquid
• malononitrile
• synthesis

ACKNOWLEDGMENTS

We are grateful to the National Natural Science Foundation of China (20802061), the Natural Science Foundation (08KJD150019), and Qing Lan Project (08QLT001) of Jiangsu Education Committee for financial support.

Notes

^a Reaction conditions: 1 mL ionic liquid, 2 mmol 2-chlorobenzaldehyde, and 2 mmol 1-phenylethylidenemalononitrile.

^b bmim, 1-butyl-3-methylimidazolium; emim, 1-ethyl-3-methylimidazolium; pmim, 1-methyl-3-propylimidazolium.

^c Isolated yields.

^d Reaction conditions: 1 mL ionic liquid, 2 mmol 2-chlorobenzaldehyde, 2 mmol 1-phenylethylidenemalononitrile, 10 mol% piperidine.

^a Reaction conditions: 1 mL ionic liquid, 2 mmol aromatic aldehyde 1, 0.2 mmol malononitrile 2, and 2 mmol 2-(1-arylethylidene)malononitrile 3, 90°C.

^b Isolated yields.