SyntheticPage 712
Published Feb 02, 2014
Procedure
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).
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SyntheticPage 773
Published Jan 06, 2015
Procedure
Preparation of 4-hydroxy phenylaldoxime: To the solution of hydroxylamine hydrochloride (1 g, 14.5 mmol) in water (10 ml) was added sodium hydroxide (307 mg, 7.6 mmol) and 4-hydroxy benzaldehyde (1.77 g, 14.5 mmol) and reaction mixture was stirred for 2 hrs at room temperature. After completion of the reaction (monitoring by TLC), if compound precipitated out, was filtered on Buckner funnel or extracted with EtOAc (3 ´ 15 ml). The obtained product was taken for next step without further purification (> 90% yield).
Procedure for synthesis of 3-(4-hydroxy phenyl) 5-phenyl-isoxazole: To the stirred solution of
4-hydroxy phenyl aldoxime (100 mg, 0.729 mmol) in DMF (3 ml) was added
N-chlorosuccinimide (161 mg, 0.875 mmol) at room temperature and reaction was stirred for 0.5 h. Then, DBU (111 mg, 0.729 mmol) and
styrene (91 mg, 0.875 mmol) were added and reaction was further stirred for 1 h. After completion of the reaction (confirmed by TLC), chilled water (20 ml) was added and product was extracted with
EtOAc (3 ´ 10 ml). The organic layer was collected, dried on anhydrous sodium sulphate and solvent was evaporated on rotary evaporator to get the crude product. The crude product was purified by silica gel (#100-200) column chromatography using 20%
EtOAc: hexane to get title compound as a white solid (138 mg; 80% yield).
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Silica-HClO4 catalyzed tandem Knoevenagel condensation and [4+2]-Diel’s-Alder cycloaddition