meso Epoxides in Asymmetric Synthesis: Enantioselective Opening by Nucleophiles in the Presence of Chiral Lewis Acids



original image

The metal center coordinates to the epoxide oxygen atom, and the chiral ligand environment enables a nucleophile to discriminate between the formally enantiotopic carbon–oxygen bonds. The method developed by W. A. Nugent functions along this principle: the reaction of a range of meso epoxides with tri-alkylsilyl azides can be catalyzed by a new chiral Lewis acid derived from zirconium and gives β-azido alcohols in very good enantiomeric excesses. Nu = N3, R1R2 = CH3, (CH2)4, etc.