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DOI: 10.1055/s-2002-33523
Effect of Fifth Coordination in Catalytic Epoxidation by a Chiral Manganese Porphyrin
Publikationsverlauf
Publikationsdatum:
17. September 2002 (online)
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Abstract
The effect of multifarious organic bases in chiral manganese porphyrin catalyzed enantioselective alkene epoxidation was investigated. For substituted pyridines, the enantioselectivity of cis-β-methylstyrene epoxidation follows a linear free energy relationship for pyridines bearing electron-donating groups. Compared to the case of no amine additive, a significant improvement in enantioselectivity from 43% ee to 81% ee for epoxidation of cis-β-methylstyrene with a 86.5% stereospecificity were observed when DMAP and KHSO5 were employed as axial ligand and oxidant respectively.
Key words
enantioselective epoxidation - metalloporphyrin - axial ligand - biomimetic oxidation
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References
General procedure for catalytic oxidation: Oxone (8 mmol), NaHCO3 (3.5 mmol), were dissolved in 4 mL deionized water with stirring. cis-β-Methylstyrene (8 mmol), catalyst 1 (0.0016 mmol), and axial ligand (0.008 mmol) were dissolved in acetonitrile (4 mL). The organic mixture was added to the aqueous mixture and the whole mixture was stirred overnight. The product mixture was extracted with diethyl ether four times and the combined extract was evaporated with a rotary evaporator. The product was analyzed by HP-6890 gas chromatography equipped with with a column, J&W Scientific cyclodex B column of 30 m length, 0.250 mm internal diameter, 0.25 µm film thickness.