ol7b02189_si_002.cif (601.89 kB)
Diastereodivergent and Enantioselective Access to Spiroepoxides via Organocatalytic Epoxidation of Unsaturated Pyrazolones
dataset
posted on 2017-09-14, 14:33 authored by Sara Meninno, Angelo Roselli, Amedeo Capobianco, Jacob Overgaard, Alessandra LattanziReadily
available chiral amine–thioureas are effective catalysts
for the first diastereo- and enantioselective epoxidation of unsaturated
pyrazolones. The trans- or cis-spiroepoxides
are preferentially obtained in good yield and high to excellent enantioselectivity
using an appropriate organocatalyst and tert-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.