J. M. Khurana and S. Kumar, “Tetrabutylammonium Bromide (TBAB): A Neutral and Efficient Catalyst for the Synthesis of Biscoumarin and 3,4-Dihydropyrano[c]-Chromene Derivatives in Water and Solvent-Free Conditions,” Tetrahedron Letters, Vol. 50, No. 28, 2009, pp. 4125- 4127. doi:10.1016/j.tetlet.2009.04.125

has been cited by the following article:

• TITLE: Silica-Grafted Ionic Liquids as Recyclable Catalysts for the Synthesis of 3,4-Dihydropyrano[c]chromenes and Pyra-no[2,3-c]pyrazoles

  AUTHORS: Khodabakhsh Niknam, Abolhassan Piran

  KEYWORDS: Silica-Grafted N-Propyl-Imidazolium Hydrogen Sulfate; Aldehydes; Pyrano[2, 3-c]-Pyrazoles; 3, 4-Dihydropyrano[c]-Chromenes; Solvent-Free, Heterogeneous Ionic Liquid Catalysts

  JOURNAL NAME: Green and Sustainable Chemistry, Vol.3 No.2A, May 17, 2013

  ABSTRACT: Silica-grafted N-propyl-imidazolium hydrogen sulfate ([Sipim]HSO4) is employed as a recyclable heterogeneous ionic liquid catalyst for the synthesis of 3,4-dihydropyrano[c]-chromenes by the reaction of aromatic aldehydes, malononitrile and 4-hydroxycoumarin at 100°C under solvent-free conditions. Also, heterogeneous ionic liquid catalyst was used for the synthesis of pyrano[2,3-c]-pyrazoles by the reaction of aromatic aldehydes, malononitrile and 3-methyl-l-phenyl-5-pyrazolone at 110°C under solvent-free conditions. The heterogeneous ionic liquid showed much the same efficiency when used in consecutive reaction runs.