π* anti-bonding C-C orbitals of the reacting alkene, providing a stabilizing delocalization of electrons. Donation of these electrons into the forming C-O σ bonds of the epoxide bonds also encourages the formation of the spiro-product (the geometry of the product is aligned as well). The planar configuration is disfavored due to lack of pi-backbonding and steric hindrance of the alkyl groups with large alkyl functional groups of the catalytic ring. The previously mentioned configurations are favored over the transition states of the opposing enantiomers because of unfavorable steric interactions between the R-alkyl groups (see below) and the ether-alkyl functional groups of the catalyst ring. The enantiomeric success of this epoxidation is relatively high compared to metal catalysts, and generally results in a high enantiomeric excess exceeding 80 percent. Reaction yield and stereoselectivity This procedure generates epoxides with high enantiomeric excesses from trans-disubstituted alkenes and trisubstituted alkenes. Cis-disubstituted alkenes and styrenes are asymmetrically epoxidized using a similar catalyst. Generation of (R,R) epoxides from corresponding alkenes increases in stereoselectivity with increased steric bulk of substituent R groups (especially in trans-olefins). See also Sharpless epoxidation References An Efficient Catalytic Asymmetric Epoxidation Method Zhi-Xian Wang, Yong Tu, Michael Frohn, Jian-Rong Zhang, and Yian Shi J. Am. Chem. Soc. 1997, 119(46), 11224-11235. () Frohn, M.; Shi, Y. Synthesis 2000, 14, 1979-2000 . (Review) Tian, H.; She, X.; Shu, L.; Yu, H.; Shi, Y. J. Am. Chem. Soc. 2000, 122, 11551-11552. () Tian, H.; She, X.; Xu, J.; Shi, Y. Org. Lett. 2001, 3, 1929-1931. () Shi Epoxidation <https://www.organic-chemistry.org/namedreactions/shi-epoxidation.shtm> Denmark, Wu, et al. "The Development of Chiral, Non-Racemic Dioxiranes for the Catalytic, Enantioselective Epoxidation of Alkenes". (13, April 1999) <https://www.thieme-connect.de/products/ejournals/pdf/10.1055/s-1999-3123.pdf> Frohn, Shi, Tu, Wang, Zhang, et al. "An Efficient Asymmetric Epoxidation Method". (8 July 1997) <http://pubs.acs.org/doi/pdf/10.1021/ja972272g> Shi, Wang, et al. "A New Type of Ketone Catalyst for Asymmetric Epoxidation". (12 September 1997). <http://pubs.acs.org/doi/pdf/10.1021/jo971701q> Epoxidation reactions Oxygen heterocycle forming reactions Organic oxidation reactions Name reactions