113543-35-4Relevant articles and documents
The asymmetric synthesis of α-amino acids. Electrophilic azidation of chiral imide enolates, a practical approach to the synthesis of (R)- and (S)-α-azido carboxylic acids
Evans, David A.,Britton, Thomas C.,Ellman, Jonathan A.,Dorow, Roberta L.
, p. 4011 - 4030 (2007/10/02)
Two complementary approaches to the asymmetric synthesis of α-amino acids have been achieved. In the initially investigated reaction sequence, the diastereoselective bromination of the illustrated boron enolate with N-bromosuccinimide was followed by stereospecific azide displacement by tetramethylguanidinium azide. The resulting α-azido carboximides may be readily purified to high diastereomeric purity by chromatography on silica. equation presented In the second reaction sequence, the illustrated potassium enolate was treated with 2,4,6-triisopropylbenzenesulfonyl azide, and the intermediate sulfonyl triazene was decomposed through an acetic acid quench to give the α-azido carboximide. The diastereoselection of the reaction as a function of R is as follows: R = Me, CH2Ph, 97:3; R = CHMe2, 98:2; R = CMe3, >99:1; R = Ph, 91:9. The important parameters of this azidation process were evaluated, and experiments were conducted to help elucidate the mechanism of the reaction. equation presented The α-azido carboximide products have been shown to be versatile α-amino acid synthons that may be readily converted to α-amino acids as well as to N-protected α-amino acid derivatives. The racemization-free removal of the chiral auxiliary was achieved in high yield both by saponification and transesterification, either before or after reduction and acylation of the azide functionality.
