Sharpless Asymmetric Epoxidation: Applications in the Synthesis of Bioactive Natural Products

This review discusses an important synthetic tool proposed by K.B. Sharpless in 1980, known as the Sharpless asymmetric epoxidation of allylic alcohols, and examines its use in the total synthesis of representative exponents of biologically active natural products. Focus is given to the synthesis of simple to highly complex secondary metabolites, including lactones, amino acids, diterpenes, and macrolides. The Sharpless approach involves the use of a catalyst, titanium tetra isopropoxide [Ti(O i Pr) 4 ], dialkyl tartrate as a chiral ligand, and tert-butyl hydroperoxide (TBHP) as an oxidizing agent. The method allows converting allylic alcohols to epoxides, which are chiral building blocks and versatile intermediates in the synthesis of natural products. The biological and synthetic importance of epoxides lies in the susceptibility of the three-membered heterocyclic ring to stereoand regioselective opening by nucleophilic or acidic reagents, providing oxygen adducts.