New Results on the Stereoselective Alkylations of Malic Acid Derivatives Supported by Molecular Modeling
作者:Michael Sefkow、Andreas Koch、Erich Kleinpeter
DOI:10.1002/hlca.200290007
日期:2002.12
The stereoselectivity of the alkylation of dialkyl malates is dependent on steric hindrance of both ester alkyl groups. It was found that the two alkyl groups have opposite effects on diastereoselectivity. Increased steric hindrance at the C(1) carboxy group increases the anti-selectivity, whereas increased steric hindrance at the C(4) carboxy group decreases it. The results are explained by comparing
苹果酸二烷基酯烷基化的立体选择性取决于两个酯烷基的空间位阻。发现两个烷基对非对映选择性具有相反的作用。在C(1)羧基上增加的空间位阻会增加抗选择性,而在C(4)羧基上增加的位阻会降低它的选择性。通过比较通过分子建模获得的烯醇化物的结构来解释结果。衍生自苄基取代的苹果酸的二氧戊环酮在C(4')上的烷基化在侧链上带有一个额外的立体异构中心,这取决于环缩醛和侧链的立体异构中心。低温下的烷基化仅与顺式发生-具有(R)-构型的侧链立体中心的-二氧戊环酮。相应的反式-二氧戊环酮和具有(S)-构型侧链立体生成中心的顺式-二氧戊环酮被原样回收。提出了通过从头算得到的整体式二氧杂环戊酮模型的基本原理。