Tertiary Aromatic Amide for Memory of Chirality: Access to Enantioenriched α-Substituted Valine
作者:Mathieu Branca、Didier Gori、Régis Guillot、Valérie Alezra、Cyrille Kouklovsky
DOI:10.1021/ja801165z
日期:2008.5.1
A new methodology for the asymmetric synthesis of quaternary alpha-substituted amino acids using memory of chirality has been developed. This strategy employs dynamic axial chirality of tertiary aromatic amides to memorize the initial chirality of an alpha-amino acid during the enolization step. Starting from L-valine, an oxazolidin-5-one containing a tertiary aromatic amide was synthesized in one step and then alkylated with various electrophiles with good yield and enantioselectivity (up to 96%). Quaternary products can be obtained enantiomerically pure by recrystallization. One-step deprotection affords enantioenriched (S)-alpha-methyl valine (ee = 94%) or enantiopure (S)-alpha-isopropyl aspartic acid (ee >99%) in only three steps starting from L-valine.