Epoxidation is treatment where an electrophilic oxidizing agent is capable of introducing a single oxygen atom to connect to both carbons of a double bond. This produces oxacyclopropanes (epoxides), which may, in turn, be converted for instance into vicinal anti diols.

Chiral epoxides are considered to be versatile building blocks and intermediates in asymmetric organic transformations. In order to build these chiral epoxides, numerous methods have been developed to produce important building blocks enantioselectively. Meanwhile, numerous highly stereoselective cinchona alkaloid-based organocatalysts have been synthesized furnishing high yields and remarkable enantiomeric excesses.

Asymmetric Epoxidation

Catalytic asymmetric epoxidation is for instance one of the most important chemical conversions used to synthesize numerous valuable chiral intermediates in the pharmaceutical, agrochemical and fine chemical industry. In particular Cinchona alkaloid based Phase Transfer Catalysts are widely used as green catalysts to establish chiral centers.  Its operational simplicity, mild reaction conditions, environmentally friendly reaction procedure, ready availability, easy recovery / reuse and the low toxicity of these catalysts makes it applicable to large-scale synthesis of complex and multi-functionalized organic molecules in industrial processes.

Also multifunctional Cinchona alkaloid-derived thiourea catalysts are of great importance in the synthesis of glycidic esters via an asymmetric epoxidation of trans-α-cyano-α,β-unsaturated esters using tert-butyl hydroperoxide (TBHP). The glycidic esters are isolated in excellent yields with complete trans-diastereocontrol and high enantioselectivity.

Using Cinchona alkaloid-derived primary amines as catalysts and aqueous hydrogen peroxide as the oxidant, highly enantioselective Weitz–Scheffer-type epoxidation and hydroperoxidation reactions of α,β-unsaturated carbonyl compounds can be achieved.

For further information pleas take a look into our free of charge Chiral Catalyst Data Base summarizing lots of examples for asymmetric epoxidation.

Example from literature

Highly enantioselective epoxidation of α,β-unsaturated ketones using amide-based Cinchona Alkaloids as hybrid phase-transfer catalyst. (Majdecki et al.; Org. Lett. 2020, 22, 8687-8691.)