Ionic Liquid as Catalyst and Reaction Medium: A Simple and Efficient Procedure for Paal–Knorr Furan Synthesis

Abstract

The ionic liquid 1-butyl-3-methyl-imidazolium hydrogen sulfate, [bmim]HSO₄, efficiently catalyzes Paal–Knorr furan synthesis without any organic solvent. A wide range of aliphatic and aromatic 1,4-diketones easily undergo condensations to form furan derivatives, providing a general and convenient procedure. The Paal–Knorr reaction of ester-substituted 1,4-diketones is first reported. The ionic liquid can be recovered and reused for subsequent runs without any appreciable loss of efficiency.

Keywords:

• Catalyst
• furan derivatives
• ionic liquid
• Paal–Knorr reaction
• reaction medium

ACKNOWLEDGMENTS

Financial support from the Scientific Research Foundation for the Returned Overseas Chinese Scholars of the State Education Ministry, the Natural Science Foundation Project of Chongqing, Chongqing Science & Technology Commission (CQ CSTC) (2006BB5377), the High-Tech Training Fund of Southwest University (XSGX0601), and the Doctoral Fund of Southwest University (SWNUB2005012) is gratefully acknowledged.

Notes

^a The reaction was carried out in a sealed tube at 150°C within an oven without stirring.

^b Yield of crude product of >95% purity by NMR.

^c Yield of isolated product after flash chromatography.