A chiral phosphazane reagent strategy for the determination of enantiomeric excess of amines
Methods for measuring enantiomeric excess ( ee ) of organic molecules by NMR spectroscopy provide rapid analysis using a standard technique that is readily available. Commonly this is accomplished by chiral derivatisation of the detector molecule (producing a chiral derivatisation agent, CDA), which...
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Published in | Chemical science (Cambridge) Vol. 13; no. 18; pp. 5398 - 5412 |
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Main Authors | , , , , , , , |
Format | Journal Article |
Language | English |
Published |
CAMBRIDGE
Royal Soc Chemistry
11.05.2022
Royal Society of Chemistry The Royal Society of Chemistry |
Subjects | |
Online Access | Get full text |
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Summary: | Methods for measuring enantiomeric excess (
ee
) of organic molecules by NMR spectroscopy provide rapid analysis using a standard technique that is readily available. Commonly this is accomplished by chiral derivatisation of the detector molecule (producing a chiral derivatisation agent, CDA), which is reacted with the mixture of enantiomers under investigation. However, these CDAs have almost exclusively been based on carbon frameworks, which are generally costly and/or difficult to prepare. In this work, a methodology based on the readily prepared inorganic cyclodiphosph(
iii
)azane CDA ClP(μ-N
t
Bu)
2
POBorn (Born =
endo
-(1
S
)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-yl) is shown to be highly effective in the measurement of
ee
's of chiral amines, involving
in situ
reaction of the chiral amines (R*NH
2
) with the P-Cl bond of the CDA followed by quaternization of the phosphorus framework with methyl iodide. This results in sharp
31
P NMR signals with distinct chemical shift differences between the diastereomers that are formed, which can be used to obtain the
ee
directly by integration. Spectroscopic, X-ray structural and DFT studies suggest that the NMR chemical shift differences between diastereomers is steric in origin, with the sharpness of these signals resulting from conformational locking of the bornyl group relative to the P
2
N
2
ring induced by the presence of the P(
v
)-bonded amino group (R*NH). This study showcases cheap inorganic phosphazane CDAs as simple alternatives to organic variants for the rapid determination of
ee
.
The simple inorganic cyclodiphosph(
iii
)azane chiral derivatisation agent ClP(μ-
t
BuN)
2
POBorn (Born =
endo
-(1
S
)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-yl) is shown to be effective in the measurement of
ee
's of chiral amines using
31
P NMR spectroscopy. |
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Bibliography: | For ESI and crystallographic data in CIF or other electronic format see Electronic supplementary information (ESI) available: synthetic procedures and analytical data, NMR and X-ray data, DFT calculations. CCDC 2157891-2157896 https://doi.org/10.1039/d2sc01692c 2105705-2105719 and ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 2041-6520 2041-6539 |
DOI: | 10.1039/d2sc01692c |