Are both the (R)- and the (S)-MPA esters really needed for the assignment of the absolute configuration of secondary alcohols by NMR?: The use of a single derivative
Are both the (R)- and the (S)-MPA esters really needed for the assignment of the absolute configuration of secondary alcohols by NMR?: The use of a single derivative
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DOI：
10.1021/ja9700055
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发表时间：
1998-02-11
影响因子：
15
通讯作者：
Riguera, R
中科院分区：
文献类型：
--
作者：
Latypov, SK;Seco, JM;Riguera, R
仲醇的绝对构型可以从在两个不同温度下记录的单一甲氧基苯乙酸酯衍生物[MPA，(R)或(S)]的H-1 NMR谱推断出来。这种新方法简化了当前基于 NMR 的方法，仅需要一次衍生反应，而不是两次，相应地，样品量也是通常量的一半。在低温下，最稳定的 sp 构象异构体的相对数量增加，位于苯环屏蔽锥下方的醇取代基 (L-1/L-2) 的共振向上场移动。与此同时，在较少的 ap 构象异构体中的屏蔽锥下方的那些质子被移动到低场。通过这种方式，通过比较室温和低温下的 H-1 NMR 谱，可以确定 L-1/L-2 围绕醇不对称中心的空间位置。介绍了这一发现在已知绝对构型的醇（包括复杂结构，如顺式雄甾酮）中的应用。
The absolute configuration of a secondary alcohol can be deduced from the H-1 NMR spectra of a single methoxyphenylacetic ester derivative [MPA, either the (R) or the (S)] recorded at two different temperatures. This new approach simplifies the current NMR-based methodologies, requiring just one derivatizing reaction, instead of two, and, correspondingly, half-of the usual amount of sample. At low temperature, the relative population of the most stable sp conformer is increased and the resonances of the substituents of the alcohol (L-1/L-2), located under the shielding cone of the phenyl ring, are shifted upfield. At the same time, those protons under the shielding cone in the less populated ap conformer are shifted downfield. In this way, the spatial location of L-1/L-2 around the asymmetric center of the alcohol can be established comparing the H-1 NMR spectra both at room and low temperatures. Application of this finding to alcohols of known absolute configuration, including complex structures such as cis-androsterone, is presented.