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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• 作者：Shamil K. Latypov ; José ; M. Seco ; Emilio Quiñ ; o&aacute ; and Ricardo Riguera
• 刊名：Journal of the American Chemical Society
• 出版年：1998
• 出版时间：February 11, 1998
• 年：1998
• 卷：120
• 期：5
• 页码：877 - 882
• 全文大小：206K
• 年卷期：v.120,no.5(February 11, 1998)
• ISSN：1520-5126

文摘

The absolute configuration of a secondary alcohol can be deducedfrom the ¹H NMR spectra of asingle methoxyphenylacetic ester derivative [MPA, either the(R) or the (S)] recorded at twodifferenttemperatures. This new approach simplifies the current NMR-basedmethodologies, requiring just onederivatizing reaction, instead of two, and, correspondingly, half ofthe usual amount of sample. At lowtemperature, the relative population of the most stable spconformer is increased and the resonances of thesubstituents of the alcohol (L₁/L₂), locatedunder the shielding cone of the phenyl ring, are shifted upfield.Atthe same time, those protons under the shielding cone in the lesspopulated ap conformer are shifted downfield.In this way, the spatial location of L₁/L₂around the asymmetric center of the alcohol can beestablishedcomparing the ¹H NMR spectra both at room and lowtemperatures. Application of this finding to alcoholsof known absolute configuration, including complex structures such ascis-androsterone, is presented.