Pronounced Steric Hindrance for Nitrogen Inversion in 1,3,4-Oxadiazolidines

Kostyanovsky, Remir G.; Кадоркина, Г. К.; Kostyanovsky, Vasilii R.; Schurig, Volker; Trapp, Oliver

doi:10.1002/1521-3773(20000818)39:16<2938::aid-anie2938>3.0.co;2-r

Cited by 45 publications

(28 citation statements)

References 25 publications

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“…Chirasil-β-Dex is one of the most versatile CSPs and is recommended as a starting point for developing and optimizing chiral separations, because a broad range of compounds, including compounds with stereogenic nitrogen (Tröger's base, 151 aziridines, diaziridines, etc. ), [152][153][154][155] can be separated with excellent separation factors α and resolution R (Table 2).…”

Section: Heptakismentioning

confidence: 99%

Chiral stationary phases and applications in gas chromatography

et al. 2022

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Chiral compounds are ubiquitous in nature and play a pivotal role in biochemical processes, in chiroptical materials and applications, and as chiral drugs. The analysis and determination of the enantiomeric ratio (er) of chiral compounds is of enormous scientific, industrial, and economic importance. Chiral separation techniques and methods have become indispensable tools to separate chiral compounds into their enantiomers on an analytical as well on a preparative level to obtain enantiopure compounds. Chiral gas chromatography and high‐performance liquid chromatography have paved the way and fostered several research areas, that is, asymmetric synthesis and catalysis in organic, medicinal, pharmaceutical, and supramolecular chemistry. The development of highly enantioselective chiral stationary phases was essential. In particular, the elucidation and understanding of the underlying enantioselective supramolecular separation mechanisms led to the design of new chiral stationary phases. This review article focuses on the development of chiral stationary phases for gas chromatography. The fundamental mechanisms of the recognition and separation of enantiomers and the selectors and chiral stationary phases used in chiral gas chromatography are presented. An overview over syntheses and applications of these chiral stationary phases is presented as a practical guidance for enantioselective separation of chiral compound classes and substances by gas chromatography.

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Section: Heptakismentioning

confidence: 99%

Chiral stationary phases and applications in gas chromatography

et al. 2022

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“…1 Unlike 3,4-dialkyl-1,3,4-oxadiazolines, 2 these hydrazines are highly chemically stable; they form stable salts with acids and iodine methylates. In a case of 3,4-di-tert-butyl-1,3,4-oxadiazolidine, nitrogen inversion occurs by a dissociative mechanism with O-CH 2 bond cleavage, 3 whereas the activation parameters of 1,2-diisopropylpyrazolidine inversion (∆G ¹ = 67.7 kJ mol -1 , ∆H ¹ = 61.1 kJ mol -1 , ∆S ¹ = -22.2 J K -1 mol -1 ) testify to a pyramidal character of the process. On the basis of a comparative analysis of inversion barriers, we suggested 1 a more than twofold increase in the inversion barrier when transferring from 1,2-diisopropylpyrazolidine to a 1,2-di-tert-butyl analogue, that would provide an opportunity for obtaining the compound in an optically active form under normal conditions.…”

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Nitrogen chirality via the sterical veto of N inversion

Usachev

Никифоров

Strelenko

et al. 2003

Mendeleev Communications

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“…2 . The equation has already been used to calculate the rate constant in dynamic three‐column chromatography [47] as well as in multidimensional stopped‐flow gas chromatography (sfMDGC) [48,49] . The enantiomerization rate constants [50] k enant are obtained according to the following equation:

true k_{e n a n t} = \frac{k_{r a c}}{2} = \frac{1}{2 Δ t} normall normaln ((), \frac{e r + 1}{e r - 1}) = \frac{1}{2 Δ t} l n ((), \frac{A_{S} + A_{normalR} + A_{S^{'}, R^{'}}}{A_{normalS} + A_{normalR} - A_{S^{'}, R^{'}}})

…”

Section: Resultsmentioning

confidence: 99%

Scorpio‐Ligand: Synthesis of Biphenyl‐Dihydroazepine Phosphoramidite Ligands for Asymmetric Hydrogenation

Auras

Trapp

2021

Helvetica Chimica Acta

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A novel dihydroazepine‐bridged BIPHEP phosphoramidite ligand with an amino acid moiety in the backbone was synthesized and evaluated in the Rh‐catalyzed asymmetric hydrogenation. The scorpion tail‐like amino acid backbone is capable of hydrogen bond formation and able to shift the rotamer composition of the biphenyl axis with the two scissor‐like arms. Pivaloyl‐l‐valine was studied as chiral selector unit and compared with pivaloylglycine as the achiral reference substance. The enantiomerization barrier of the pivaloylglycine‐modified biphenylamide was determined to be ΔG≠=110 kJ/mol. In the case of pivaloyl‐l‐valine, the (Sax) isomer is thermodynamically favored. Due to the relatively high barrier, the ligand is atropisomeric at room temperature and allows the preparative separation of the stereoisomers. The obtained phosphoramidite ligands were separated by chiral HPLC. For the first eluting rotamer, Rh complex ([Rh(cod)(L)2]BF4) was generated in situ and examined in the enantioselective hydrogenation of 2‐acetamidoacrylate and methyl 2‐acetamido‐3‐phenylacrylate, achieving enantiomeric excesses of up to 94 %.

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Pronounced Steric Hindrance for Nitrogen Inversion in 1,3,4-Oxadiazolidines

Cited by 45 publications

References 25 publications

Chiral stationary phases and applications in gas chromatography

Chiral stationary phases and applications in gas chromatography

Nitrogen chirality via the sterical veto of N inversion

Scorpio‐Ligand: Synthesis of Biphenyl‐Dihydroazepine Phosphoramidite Ligands for Asymmetric Hydrogenation

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