Application of the asymmetric hydrogenation of enamines to the preparation of a beta-amino acid pharmacophore
作者:Michele Kubryk、Karl B. Hansen
DOI:10.1016/j.tetasy.2005.12.016
日期:2006.1
(3R)-3-[N-(tert-Butoxycarbonyl)amino]-4-(2,4,5-trifluorophenyt) butanoic acid 7a has been synthesized by an asymmetric hydrogenation of enamine ester 3 using chiral ferrocenyl ligands I and II in conjunction with [Rh(COD)Cl](2). The direct reduction of 3 provides amino ester 1b in 93% ee, which was isolated as an (S)-camphorsulfonic acid salt to upgrade the enantiomeric excess to > 99%. A more concise approach was developed involving the in situ protection of 1b using di-tert-butyldicarbonate. This approach provided the desired N-Boc amino ester 7b directly from the hydrogenation with 97% ee, which was upgraded to > 99% ee upon crystallization. (c) 2006 Published by Elsevier Ltd.
(3R)-3-[N-(叔丁氧基羰基)氨基]-4-(2,4,5-三氟苯基)丁酸7a是通过使用手性五氟配体I和II以及[Rh(COD)Cl]₂对烯胺酯3进行不对称氢化而合成的。直接还原3得到氨基酯1b,ee值为93%,随后将其分离为(S)-樟脑磺酸盐以将对映体过量提升至>99%。还开发了一种更简洁的方法,涉及使用双特丁基碳酸酯对1b进行原位保护。该方法通过氢化直接提供目标N-Boc氨基酯7b,ee值为97%,在结晶后ee值提升至>99%。©2006 Elsevier Ltd.出版。