Isolation and enantiostability of the B-chiral bis(salicylato)borate anions [BR(Sal)2] and [BS(Sal)2]†
a
and
Ian D.
Williams
*a
Abstract
The chiral spiroborate anions [BS(Sal)2] and [BR(Sal)2], (R and S subscripts indicate boron stereochemistry) have been isolated as 1 : 1 quininium and 1 : 2 sparteinium salts, [HQuin][BS(Sal)2] and [H2Spa][BR(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 [NBu4][BR(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 [H2Spa][BR(Sal)2]2 is limited to 70% ee, however an enantiopure analogue [H2Spa][BR(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.
![Graphical abstract: Isolation and enantiostability of the B-chiral bis(salicylato)borate anions [BR(Sal)2] and [BS(Sal)2]](/en/Image/Get?imageInfo.ImageType=GA&imageInfo.ImageIdentifier.ManuscriptID=C7RA11997F&imageInfo.ImageIdentifier.Year=2018)
Please wait while we load your content...
