Diastereodivergent and Enantioselective Access to
Spiroepoxides via Organocatalytic Epoxidation of Unsaturated Pyrazolones
Sara Meninno
Angelo Roselli
Amedeo Capobianco
Jacob Overgaard
Alessandra Lattanzi
10.1021/acs.orglett.7b02189.s003
https://acs.figshare.com/articles/journal_contribution/Diastereodivergent_and_Enantioselective_Access_to_Spiroepoxides_via_Organocatalytic_Epoxidation_of_Unsaturated_Pyrazolones/5406679
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available chiral amine–thioureas are effective catalysts
for the first diastereo- and enantioselective epoxidation of unsaturated
pyrazolones. The <i>trans</i>- or <i>cis</i>-spiroepoxides
are preferentially obtained in good yield and high to excellent enantioselectivity
using an appropriate organocatalyst and <i>tert</i>-butyl
hydroperoxide as the oxidant. The epoxidation appears applicable to
highly challenging β,β′-substituted unsaturated
pyrazolones, giving access to spiroepoxides bearing two vicinal quaternary
stereocenters. The reaction represents a unique example of Weitz–Scheffer
epoxidation, where the catalyst-controlled ring-closure step is usefully
exploited to prepare both enantioenriched diastereomeric epoxides.
2017-09-14 14:33:10
enantioenriched diastereomeric epoxides
enantioselective epoxidation
Unsaturated Pyrazolones
pyrazolone
vicinal quaternary stereocenters
butyl hydroperoxide
Enantioselective Access
Organocatalytic Epoxidation
spiroepoxide
catalyst-controlled ring-closure step