Novel strategy for the synthesis of fluorinated β-amino acid derivatives from Δ2-oxazolines
摘要:
Racemic and chiral non-racemic beta -fluoroalkyl-beta -amino acid derivatives have been prepared in two steps starting from 2-alkyl-Delta (2)-oxazolines and fluorinated imidoyl chlorides. Subsequent chemoselective reduction of the C-masked beta -enamino acid derivatives initially formed provided the target beta -amino acids. The process takes place with total chemoselectivity, high yields and satisfactory diastereoselectivity. (C) 2001 Elsevier Science Ltd. All rights reserved.
Novel strategy for the synthesis of fluorinated β-amino acid derivatives from Δ2-oxazolines
摘要:
Racemic and chiral non-racemic beta -fluoroalkyl-beta -amino acid derivatives have been prepared in two steps starting from 2-alkyl-Delta (2)-oxazolines and fluorinated imidoyl chlorides. Subsequent chemoselective reduction of the C-masked beta -enamino acid derivatives initially formed provided the target beta -amino acids. The process takes place with total chemoselectivity, high yields and satisfactory diastereoselectivity. (C) 2001 Elsevier Science Ltd. All rights reserved.
New Strategy for the Stereoselective Synthesis of Fluorinated β-Amino Acids
作者:Santos Fustero、Belén Pina、Esther Salavert、Antonio Navarro、M. Carmen Ramírez de Arellano、Antonio Simón Fuentes
DOI:10.1021/jo025621k
日期:2002.7.1
Racemic and chiral nonracemic alpha-substituted and alpha-unsubstituted beta-fluoroalkyl beta-amino acid derivatives 6 and 9 have been synthesized in two steps starting from fluorinated imidoyl chlorides 1 and ester enolates. This approach is based on the chemical reduction of previously obtained gamma-fluorinated beta-enamino esters 4 by using ZnI2/NaBH4 in a nonchelated aprotic medium (dry CH2Cl2) as the reducing agent. A metal-chelated six-membered model has been suggested to explain the stereochemical outcome of the reduction reaction. The process takes place with high yields and with moderate to good diastereoselectivity. The best results related to diastereoselective reduction of chiral beta-enamino esters 4 were provided by the use of (-)-8-phenylmenthol as a chiral auxiliary.