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.
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.