Opportunities for insiders: A catalytic pinacol-type reductiverearrangement of 1,2-internal diols was developed by the use of a simple boron catalyst and two silanes (see scheme). The reaction occurs through a concerted, stereoinvertive mechanism and is applicable to several substrate scaffolds not usually amenable to pinacol-type reactions, such as aliphatic secondary–secondary diols, without the
Deracemization of (±)-2,3-disubstituted oxiranes via biocatalytic hydrolysis using bacterial epoxide hydrolases: kinetics of an enantioconvergent process
作者:Wolfgang Kroutil、Martin Mischitz、Kurt Faber
DOI:10.1039/a704812b
日期:——
Asymmetric biocatalytichydrolysis of (±)-2,3-disubstituted oxiranes leading to the formation of vicinal diols in up to 97% ee at 100% conversion was accomplished by using the epoxide hydrolase activity of various bacterial strains. The mechanism of this deracemization was elucidated by 18OH2-labelling experiments using a partially purified epoxide hydrolase from Nocardia EH1. The reaction was shown
Determining the Absolute Stereochemistry of Secondary/Secondary Diols by <sup>1</sup>H NMR: Basis and Applications
作者:Félix Freire、José Manuel Seco、Emilio Quiñoá、Ricardo Riguera
DOI:10.1021/jo048643a
日期:2005.5.1
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 chemicalshifts of the signals for substituents
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bis-(R)和双(S)-MPA酯。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包括比较取代基R 1 / R 2和连接在两个手性中心[ Hα(双-(R)-和双-(S)-酯中的R 1)和Hα(R 2)]表示为Δδ。RS理论计算[通过半经验(AM1),从头算(HF),DFT(B3LYP)和Onsager方法进行的能量最小化,以及芳香族屏蔽效应的计算]和实验数据(NMR和CD光谱)表明,在这些bis-MPA酯中,实验Δδ RS值是两个MPA单元根据二醇的实际立体化学结合而产生的屏蔽/去屏蔽效果的结果。用MPA和9-AMA作为辅助试剂衍生的各种已知绝对构型的二醇证明了这些相关性的可靠性。一个简单的图形模型,其允许1的两个不对称碳的同时分配,Ñ二醇由NMR光谱的比较(Δδ RS给出了其双-(R)
Bartels Birgit, Hunter Roger, J. Org. Chem, 58 (1993) N 24, S 6756-6765
作者:Bartels Birgit, Hunter Roger
DOI:——
日期:——
13C NMR as a general tool for the assignment of absolute configuration
作者:Iria Louzao、José Manuel Seco、Emilio Quiñoá、Ricardo Riguera
DOI:10.1039/c0cc02774j
日期:——
(13)C NMR, alone or in combination with (1)H NMR, allows the assignment of the absolute configuration of chiral alcohols, amines, carboxylic acids, thiols, cyanohydrins, sec,sec-diols and sec,sec-aminoalcohols, derivatized with appropriate chiral auxiliaries. This extends the assignment possibilities of NMR to fully deuterated and to nonproton containing compounds.