scholarly journals Synthesis, Resolution and Absolute Configuration of 2,3-Dihydro-2-<i>Tert</i>-Butyl-3-<i>N</i>-Benzylquinazolin-4-One: A Possible Chiral Auxiliary for Synthesis of <i>β</i>-Amino Cyclohexancarboxylic Acid

2014 ◽  
Vol 04 (01) ◽  
pp. 48-54
Author(s):  
Fanny A. Cabrera-Rivera ◽  
Jaime Escalante
Keyword(s):  
Absolute Configuration ◽  
Chiral Auxiliary

The Theoretical Basis for Assignment by NMR

2015 ◽  
Author(s):  
Josi M. Seco ◽  
Emilio Quiqoa ◽  
Ricardo Riguera
Keyword(s):  
Absolute Configuration ◽  
Chiral Auxiliary ◽  
Primary Amines ◽  
Primary Alcohols ◽  
Chiral Reagent ◽  
Chiral Compounds ◽  
Configurational Assignment ◽  
Derivatizing Agent ◽  
Chiral Derivatizing Agent ◽  
Diastereomeric Complexes

The nuclear magnetic resonance (NMR) spectra of two enantiomers are identical. Thus, the first step in using NMR to distinguish between two enantiomers should be to produce different spectra that eventually can be associated with their different stereochemistry (i.e., the assignment of their absolute configuration). Therefore, it is necessary to introduce a chiral reagent in the NMR media. There are two ways to address this problem. One is to use a chiral solvent, or a chiral agent, that combines with each enantiomer of the substrate to produce diastereomeric complexes/associations that lead to different spectra. This is the so-called chiral solvating agent (CSA) approach; it will not be further discussed here [33–34]. The second approach is to use a chiral auxiliary reagent [13–15] (i.e., a chiral derivatizing agent; CDA) that bonds to the substrate by a covalent linkage. Thus, in the most general method, the two enantiomers of the auxiliary CDA react separately with the substrate, giving two diastereomeric derivatives whose spectral differences carry information that can be associated with their stereochemistry. The CDA method that employs arylalcoxyacetic acids as auxiliaries is the most frequently used. It can be applied to a number of monofunctionals [14–15] (secondary alcohols [35–43], primary alcohols [44–46], aldehyde [47] and ketone cyanohydrins [48–49], thiols [50–51], primary amines [52–56], and carboxylic acids [57–58]), difunctional [13] (sec/sec-1,2-diols [59–61], sec/sec-1,2-amino alcohols [62], prim/sec-1,2-diols [63–65], prim/sec-1,2-aminoalcohols, and sec/prim-1,2-aminoalcohols [66–68]), and trifunctional (prim/sec/sec-1,2,3-triols [13, 69–70]) chiral compounds. Its scope and limitations are well established, and its theoretical foundations are well known, making it a reliable tool for configurational assignment. Figure 1.1 shows a summary of the steps to be followed for the assignment of absolute configuration of a chiral compound with just one asymmetric carbon and with substituents that, for simplicity, are assumed to resonate as singlets. Step 1 (Figure 1.1a): A substrate of unknown configuration (?) is separately derivatized with the two enantiomers of a chiral auxiliary reagent, (R)-Aux and (S)-Aux, producing two diastereomeric derivatives.

scholarly journals Determination of absolute configuration of secondary alcohols using new chiral auxiliary and chemical shift calculation

2006 ◽  
Vol 47 (10) ◽  
pp. 1519-1523 ◽  
Author(s):  
Hajime Iwamoto ◽  
Yuka Kobayashi ◽  
Takefumi Kawatani ◽  
Masataka Suzuki ◽  
Yoshimasa Fukazawa
Keyword(s):  
Chemical Shift ◽  
Absolute Configuration ◽  
Chiral Auxiliary ◽  
Secondary Alcohols ◽  
Determination Of Absolute Configuration ◽  
Shift Calculation

Determining the absolute configuration of secondary alcohols by means of a chiral auxiliary and NOESY

2005 ◽  
Vol 16 (24) ◽  
pp. 3976-3985 ◽  
Author(s):  
Blanca E. Domínguez ◽  
Patricia E. García ◽  
Jorge Cárdenas
Keyword(s):  
Absolute Configuration ◽  
Chiral Auxiliary ◽  
Secondary Alcohols ◽  
The Absolute

New rare atropisomers: structure elucidation, absolute configuration and antimicrobial activity

Planta Medica ◽  
2011 ◽  
Vol 77 (12) ◽  
Author(s):  
A Debbab ◽  
R Bara ◽  
A Pretsch ◽  
R Edrada Ebel ◽  
V Wray ◽  
...  
Keyword(s):  
Antimicrobial Activity ◽  
Absolute Configuration ◽  
Structure Elucidation
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