An efficient synthesis of chiral syn-α,γ-dihydroxycarbonyl units from readily available achiral precursors in three pots under mild conditions was developed. This method explored the asymmetric direct cross-aldol reaction of two different aldehydes in the presence of an organocatalyst to generate a chiral β-hydroxyaldehyde, which was converted into a 4-nitromethyl-1,3-dioxane derivative as a diastereo-mixture via a sequence of nitroalkane addition and acetalization. The 4-nitromethyl-1,3-dioxane derivative was then transformed either to a carboxylic ester or to an aldehyde/ketone. The chiral syn-α,γ-dialkoxy esters and aldehydes/ketones were all obtained with excellent enantiopurity and diastereoselectivity after a base-promoted epimerization.
本研究开发了一种在温和条件下,通过三个罐子从容易获得的非手性前体中高效合成手性合成-α,γ-二羟基羰基单元的方法。该方法探索了在有机催化剂存在下两种不同醛的不对称直接交醛反应,生成手性 β-羟基醛,通过一连串的硝基
烷烃加成和
缩醛反应将其转化为 4-硝基甲基-
1,3-二氧六环衍
生物的非对映混合物。然后,4-硝基甲基-1,3-
二恶烷衍
生物被转化为
羧酸酯或醛/酮。经过碱促进的外延化反应后,得到的手性合成-α,γ-二烷氧基酯和醛/酮都具有极好的对映体纯度和非对映选择性。