Meso Epoxides Research Articles

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

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.

Preparation of proline derived lithium amide bases and their use in enantioselective deprotonation of meso epoxides

An alternative method of preparation for a range of proline derived chiral lithium amide bases is described. (S)-2-(Pyrrolidinomethyl) pyrrolidine, prepared by the new route, has been used to deprotonate cis and trans tbutyldimethylsiloxy-3,4-epoxycyclopentane enantioselectively, thus generating chiral cis and trans tbutyldimethylsiloxy-2-cyclopenten-4-ols. The products had higher enantiomeric purity than those produced when the base was prepared by a previously reported method.