A U-turn in the Asymmetric Appel Reaction
2.0 m solution in THF, 1.5 mmol) was added. 31P NMR spec-
troscopy analysis of the clear solution revealed one peak for the
phosphane borane at δ = 10.1 ppm. A portion of the reaction mix-
ture was removed, concentrated under reduced pressure, diluted in
HPLC mobile phase, filtered though a 0.2-μm Millipore Acrodisc
and directly injected (10 μL) onto the HPLC system (see the Sup-
porting Information) for ee analysis. The remaining reaction mix-
ture was diluted with EtOAc (15 mL) and water (10 mL). The or-
ganic layer was separated, and the aqueous layer was extracted with
EtOAc (10 mL). The combined organic extracts were dried with
MgSO4 and concentrated under reduced pressure. The residue was
passed through a column of basic alumina by using degassed Et2O.
The solvent was removed under vacuum and column chromatog-
raphy was carried out on silica gel (EtOAc, Rf = 0.11) to yield the
enantioenriched phosphane borane as a white solid [0.20 g, 96%,
79%ee (R)].
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(c) Optimized Procedure for NaBH4 Reduction with Methyl(phenyl)-
o-tolylphosphane as Example: Experimental procedure as per sec-
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spectroscopy. To the mixture was added a solution of NaBH4
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phane borane formed (31P NMR signal at δ = 10.1 ppm). Workup
and analysis as per section (b) gave the enantioenriched phosphane
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Acknowledgments
We sincerely thank Science Foundation Ireland (SFI) for funding
this research under grants 08/RFP/CHE1251 and 09/IN.1/B2627.
We are also grateful to the Centre for Synthesis and Chemical Bio-
logy and the UCD School of Chemistry and Chemical Biology for
access to their extensive analysis facilities.
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Received: March 7, 2012
Published Online: April 5, 2012
Eur. J. Org. Chem. 2012, 2720–2723
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
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