Silica-HClO4 catalyzed tandem Knoevenagel condensation and [4+2]-Diel’s-Alder cycloadditionSilica-HClO4 catalyzed tandem Knoevenagel condensation and [4+2]-Diel’s-Alder cycloaddition
SyntheticPage 712
Published Feb 02, 2014
Preparation of Silica-HClO4 catalyst: Perchloric acid (1.25 g, as a 70% aqueous solution) was added to the suspension of silica gel (23.75 g, mesh 230–400) in Et2O. The mixture was concentrated and the residue was heated at 100 °C for 72 h under vacuum to afford HClO4–SiO2 as a free flowing powder. http://dx.doi.org/10.1039/B304178F
To the solution of 2,4-diacetyl phloroglucinol (100 mg, 1 mmol) in acetonitrile (10 mL) were added formaldehyde (0.04 mL, 3 mmol), styrene (74 mg, 1.5 mmol) and 50 %w/w silica-HClO4 (50 mg). The mixture was then heated to reflux at 80 °C for 6 h. Completion of the reaction was monitored by TLC (by disappearance of 2,4-diacetyl phloroglucinol on TLC). After completion of the reaction, the mixture was cooled to room temperature and was filtered through filter paper. The filtrate was concentrated on a rotary evaporator to give the crude product as a colourless oil. Purification by silica gel (mesh 100-200) column chromatography using EtOAc: Hexane - 1:1 as eluent gave product as white crystals (84% yield).