Isolation and enantiostability of the B-chiral bis(salicylato)borate anions [BR(Sal)2] and [BS(Sal)2]Electronic supplementary information (ESI) available. CCDC 1581657-1581661 and 1581667. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c7ra11997f
The chiral spiroborate anions [B S (Sal) 2 ] and [B R (Sal) 2 ], ( R and S subscripts indicate boron stereochemistry) have been isolated as 1 : 1 quininium and 1 : 2 sparteinium salts, [HQuin][B S (Sal) 2 ] and [H 2 Spa][B R (Sal) 2 ] 2 respectively, by either cation metathesis or a simple one-pot s...
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Main Authors | , , , , , , , |
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Format | Journal Article |
Published |
04.01.2018
|
Online Access | Get full text |
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Summary: | The chiral spiroborate anions [B
S
(Sal)
2
] and [B
R
(Sal)
2
], (
R
and
S
subscripts indicate boron stereochemistry) have been isolated as 1 : 1 quininium and 1 : 2 sparteinium salts, [HQuin][B
S
(Sal)
2
] and [H
2
Spa][B
R
(Sal)
2
]
2
respectively, by either cation metathesis or a simple one-pot synthesis involving reaction of boric and salicylic acids with the alkaloid base. Circular dichroism (CD) spectroscopy shows that the B-based chirality is stable in polar aprotic media, such as DMF or DMSO, though labile in protic solutions. Enantiopure salts with achiral counter-cations such as [NBu
4
][B
R
(Sal)
2
] may then be prepared by exchange, so these B-chiral anions may have use in metathesis-based resolutions. Due to a site disorder the anion in [H
2
Spa][B
R
(Sal)
2
]
2
is limited to 70% ee, however an enantiopure analogue [H
2
Spa][B
R
(5-Cl-Sal)
2
]
2
is readily formed using 5-chlorosalicylic acid. This also indicates a wide family of stable enantiopure B-chiral anions may be isolated by this approach.
Both chiral hands of bis(salicylato)borate anion [B
S
(Sal)
2
] and [B
R
(Sal)
2
] are isolated and CD spectroscopy indicates they can be configurationally stable. |
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Bibliography: | Electronic supplementary information (ESI) available. CCDC 10.1039/c7ra11997f For ESI and crystallographic data in CIF or other electronic format see DOI 1581667 and 1581657-1581661 |
ISSN: | 2046-2069 |
DOI: | 10.1039/c7ra11997f |