An Efficient Enantioselective Method for Asymmetric Friedel–Crafts Alkylation
FULL PAPERS
was quenched with saturated aqueous NH4Cl. The organic
materials were extracted with AcOEt and dried over anhy-
drous Na2SO4, then concentrated under reduced pressure.
The residue was purified by silica gel column chromatogra-
phy to afford 5. The enantioselectivity was determined by
subjecting approximately 10 mg of the title compound to an
excess of NaBH4 and 1 mL of methanol. After 30 min, the
solution was treated with saturated aqueous NaHCO3, and
the mixture was extracted with CH2Cl2. The organic layer
was separated, filtered through a silica gel plug and subject-
ed to chiral HPLC analysis (conditions noted). The absolute
configuration of adducts was assigned by comparison to the
literature data.[9b]
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Acknowledgements
We are grateful for the financial support from the National
Natural Science Foundation of China (Nos. 20525206,
20772052 and 20621091), and Chang Jiang Scholar Program
of the Ministry of Education of China.
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