Metal-free DBU promoted cycloaddition of styrene to hydroxylimineMetal-free DBU promoted cycloaddition of styrene to hydroxylimine
SyntheticPage 773
Published Jan 06, 2015
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).