Determining the absolute stereochemistry of secondary/secondary diols by 1H NMR: Basis and applications
Determining the absolute stereochemistry of secondary/secondary diols by 1H NMR: Basis and applications
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DOI：
10.1021/jo048643a
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发表时间：
2005-05-13
影响因子：
3.6
通讯作者：
Riguera, R
中科院分区：
文献类型：
--
作者：
Freire, F;Seco, JM;Riguera, R
由两个仲（手性）羟基形成的1，2-、1，3-、1，4-和1，5-二醇的绝对构型可以通过比较相应的双-（R）-和双（S）-MPA酯的NMR谱来推断。双酯衍生物的NMR光谱与二醇的绝对立体化学之间的相关性涉及取代基R-1/R-2的信号和连接到双-（R）-酯和双-（S）-酯中的两个手性中心[H-α（R-1）和H-α（R-2）]的氢的信号的化学位移的比较，并表示为Δ Δ。(RS)理论计算[通过半经验（AM 1）、从头算（HF）、DFT（B3 LYP）和Onsager方法的能量最小化以及芳香族屏蔽效应计算]和实验数据（NMR和CD光谱）表明在这些双-MPA酯中，实验Δ Δ（RS）值是屏蔽/由根据二醇的实际立体化学联合收割机结合的两个MPA单元产生的去屏蔽效应。证明了这些相关性的可靠性与广泛的已知的绝对配置的二醇衍生MPA和9-AMA作为辅助试剂。提出了一个简单的图形模型，可以通过比较其双-（R）-和双-（S）AMAA酯衍生物的NMR光谱（Delta Delta（RS）符号）来同时指定1，n-二醇的两个不对称碳。
The absolute configuration of 1,2-, 1,3-, 1,4-, and 1,5-diols formed by two secondary (chiral) hydroxy groups can be deduced by comparison of the NMR spectra of the corresponding bis-(R)- and bis(S)-MPA esters. The correlation between the NMR spectra of the bis-ester derivatives and the absolute stereochemistry of the diol involves the comparison of the chemical shifts of the signals for substituents R-1/R-2 and for the hydrogens attached to the two chiral centers [H-alpha(R-1) and H-alpha(R-2)] in the bis-(R)- and the bis-(S)-ester and is expressed as Delta delta.(RS) Theoretical calculations [energy minimization by semiempirical (AM1), ab initio (HF), DFT (B3LYP), and Onsager methods, and aromatic shielding effect calculations] and experimental data (NMR and CD spectroscopy) indicate that in these bis-MPA esters, the experimental Delta delta(RS) values are the result of the contribution of the shielding/deshielding effects produced by the two MPA units that combine according to the actual stereochemistry of the diol. The reliability of these correlations is demonstrated with a wide range of diols of known absolute configuration derivatized with MPA and 9-AMA as auxiliary reagents. A simple graphical model that allows the simultaneous assignment of the two asymmetric carbons of a 1,n-diol by comparison of the NMR spectra (Delta delta(RS) signs) of its bis-(R)- and bis-(S)AMAA ester derivatives is presented.