Synthesis of Enantiomerically Pure<scp>D</scp>- and<scp>L</scp>-(Heteroaryl)alanines by asymmetric hydrogenation of (<i>Z</i>)-α-amino-αβ-didehydro esters
作者:Thierry Masquelin、Emil Broger、Klaus Müller、Rudolf Schmid、Daniel Obrecht
DOI:10.1002/hlca.19940770518
日期:1994.8.10
Isomerically pure (Z)-α-amino-α,β-didehydro esters were required to obtain the highest enantiomeric excesses (ee's) in the asymmetric hydrogenation, and the tert-butyl-ester strategy was beneficial in terms of both getting pure (Z)-α-amino-α,β-didehydro esters and obtaining high ee's in the hydrogenation. Finally, in contrast to the methyl-ester series, deprotection of the tert-butyl esters 4a–d, g was easily
由二磷杂铑催化剂催化的各种甲基和叔丁基(Z)-2-(酰基氨基)-3-(杂芳基)丙烯酸酯的均相不对称氢化反应(见1a-f和2a-d,f,g,分别)对合成对映体纯的3-呋喃基,3-噻吩基和3-吡咯基丙氨酸进行了研究(参见3a–f和4a–d,g;方案1)。使用磷酸甘氨酸酯法(方案1)以高收率制备了前体(Z)-α-氨基-α,β-二氢化酯1a-f和2a-d,f,g。异构纯(Z)-α-氨基-α,β-二氢化酯需要获得不对称氢化中最高的对映体过量(ee's),而叔丁基酯策略从获得纯净的(Z)-α-氨基-α,β-二氢氢化酯,在氢化反应中获得较高的ee值。最后,与甲基酯系列相反,叔丁基酯4a-d,g的脱保护很容易使用CF 3 CO 2 H进行,没有任何消旋作用。