A highly diastereo- and enantioselective [4 + 1] cycloaddition of -quinone methides to α-halogenated ketones was realized by bifunctional phosphonium salt catalysis, furnishing functionalized 2,3-dihydrobenzofurans in high yields and excellent stereoselectivities (>20:1 and up to >99.9% ee). Mechanistic observations suggested that the reaction underwent a cascade intermolecular substitution/intramolecular 1,6-addition process. DFT calculations revealed the presence of multiple H-bonding interactions between the catalyst and the enolate intermediate in the stereodetermining transition states.
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Article Synopsis
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- The reaction achieves significant stereoselectivity, producing 23 different cyclopentanes with high enantiomeric ratios (most over 95:5) and good yields.
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