"The diphenyl prolinol\/TBHP system has been used to perform a stereoselective organocatalytic epoxidation of a series of α-alkylideneoxindoles, electron-poor olefins bearing two EWG on the opposite sides of the double bond. We always achieved the desired spiroepoxides in excellent yields and quite good enantioselectivity (up to 96%ee). This demonstrated the action mode of noncovalent catalysis that relies on a H-bond network among substrate, bifunctional catalyst and oxidant."
Gasperi, T., Palumbo, C., Mazziotta, A., Miceli, M., Loreto M., A., Gambacorta, A. (2013). Non-covalent Organocatalysis: An Open door in the Asymmetric Nucleophilic Epoxidation. In 14th Tetrahedron Symposium..