尽管丙酮酸在生物转化中发挥着重要作用,但丙酮酸盐在催化不对称合成领域的利用却出人意料地受到限制。这一说法也适用于烯胺催化,其中丙酮酸盐似乎是具有挑战性的底物。最近,文献中首次报道了丙酮酸在 NahE 酶的催化下,利用烯胺机制不对称加成到 β-硝基苯乙烯上的情况。现在,我们证明基于吡咯烷的催化剂可以模仿该酶使用的烯胺机制,在结构多样的硝基烯烃的不对称加成中激活丙酮酸,产生高度对映体富集的迈克尔加合物,而不受与生物催化剂相关的底物结构的限制。除了证实光学纯吡咯烷可以作为丙酮酸活化中的最终小型有机催化剂之外,我们还提出了一种极其简单且通用的合成光学纯γ-硝基酸的方法,γ-硝基酸是众所周知的活性药物成分(即 GABA)的前体衍生品
A practical synthesis of optically active δ-nitro-α-ketoesters and 4-cyclohexyl-proline catalyzed by chiral squamides
摘要:
Inexpensive and readily available squamides derived from 9-amino-9-deoxyepiquinine or 9-amino-9-deoxyepiquinidine were found to be superior catalysts for the asymmetric conjugate additions of t-butyl nitroacetate to beta,gamma-unsaturated-alpha-ketoesters. After the subsequent decarboxylation with silica gel, a variety of delta-nitro-alpha-ketoesters were obtained in good yields and with excellent enantioselectivities. The products were further transformed into ethyl 4-aryl-prolinate via a cascade nitro reduction and amination. A new synthesis of (2S,4S)-4-cyclohexyl-proline was also developed. A practical synthesis of optically active delta-nitro-alpha-ketoesters and 4-aryl-proline derivatives is described. (c) 2015 Elsevier Ltd. All rights reserved.