Highly Diastereoselective Lithiation and Substitution of an (S)-ProIinyl Thiocarbamate via Sterically Homogeneous Lithio(thiocarbamate);Synthesis of Enantiomerically Pure Prolinethiols

摘要

Highly diastereoselective lithiation-substitution reactions of an (S)-proline derived S-alkyl thiocarbamate was accomplished.The configuration of the predominant alkyllithium species and the stereochemical course of the electrophil-ic substitution reactions are deduced by a combination of X-ray crystal structure analysis,NMR spectroscopic studies,deuteration/dedeuteration experiments,and quantum chemical calculations.The lithium intermediate (S,S)-9 was found to be kinetically and thermodynamically favoured,whereas (S,R)-9 rapidly epimerizes.