S. S. Al Sulaimi, K. V. Rajendran, D. G. Gilheany
FULL PAPER
small scale (see Supporting Information for 31P NMR and HPLC
data).
09/IN.1/B2627. The authors are also grateful to the UCD Centre
for Synthesis and Chemical Biology (CSCB) and the UCD School
of Chemistry for access to their extensive analysis facilities.
S. A.-S. also sincerely thanks the University of Nizwa, Oman and
the Erasmus Mundus Gulf Countries Programme for scholarship
funding.
The procedure with methyl(phenyl)(o-tolyl)phosphane 1a was also
repeated in a similar manner on a larger scale: phosphane stock
solution (47.0 mL, 4.7 mmol, 0.10 m, 1.0 equiv.); (–)-menthol stock
solution (47.0 mL, 6.4 mmol, 0.137 m, 1.2 equiv.) and HCA stock
solution (47 mL, 4.7 mmol, 0.10 m, 1.0 equiv.) to yield 0.89 g (83%)
of product (78% ee) after column chromatography.
[1] a) Catalytic Asymmetric Synthesis (Ed.: I. Ojima), 3rd ed.,
Wiley-VCH, New York, 2010; b) S. J. Connon, Angew. Chem.
Int. Ed. 2006, 45, 3909–3912; Angew. Chem. 2006, 118, 4013–
4016; c) Phosphorus Ligands in Asymmetric Catalysis, vol. I–
III (Ed.: A. Börner), Wiley-VCH, Weinheim, Germany, 2008;
d) S. Lühr, J. Holz, A. Börner, ChemCatChem 2011, 3, 1708–
1730.
Scalemic-methyl(phenyl)(o-tolyl)phosphane–Borane (1b): (0.89 g,
1
83%), H NMR (CDCl3, 400 MHz): δ = 7.71–7.15 (m, 9 H, Ar),
2.17 (s, 3 H, ArCH3), 1.83 (d, 2JPH = 9.9 Hz, 3 H, CH3), 1.68–0.77
(br., 3 H, BH3) ppm. 31P NMR (CDCl3, 162 MHz): δ = 10.3 ppm.
(ref.[6a] 10.2) ppm.
Synthesis of Scalemic Phosphane–Boranes from Racemic Phosphane
Oxides
[2] For the methyl phosphinate route, see: O. Korpium, K. Mislow,
J. Am. Chem. Soc. 1967, 89, 4784–4786; B. D. Gatineau, L.
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iel, S. Jugé, in: Phosphorus Ligands in Asymmetric Catalysis
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York, 2008, vol. 3, p. 1211–1233; ring opening of tert-butylox-
azaphospholidine: T. Leon, A. Riera, X. Verdaguer, J. Am.
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Muci, K. R. Campos, D. A. Evans, J. Am. Chem. Soc. 1995,
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13922–13927; J. Granander, F. Secci, S. J. Canipa, P. O’Brien,
B. Kelly, J. Org. Chem. 2011, 76, 4794–4799; enzymatic resolu-
tion: P. Kielbasinski, J. Omelanczuk, M. Mikolajczyk, Tetra-
hedron: Asymmetry 1998, 9, 3283–3287; dynamic resolution of
racemic lithiated secondary phosphane–boranes: B. Wolfe, T.
Livinghouse, J. Am. Chem. Soc. 1998, 120, 5116; H. Heath, B.
Wolfe, T. Livinghouse, S. K. Bae, Synthesis 2001, 2341–2347;
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7189; catalytic asymmetric synthesis: C. Scriban, D. S. Glueck,
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Bergman, F. D. Toste, J. Am. Chem. Soc. 2007, 129, 15122–
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G. Cedric, S. J. Canipa, P. O’Brien, S. Taylor, J. Am. Chem.
Soc. 2006, 128, 9336–9337; designed, highly efficient diastereo-
selective synthesis via chiral benzoxazaphosphinine oxide relay:
Z. S. Han, N. Goyal, M. A. Herbage, J. D. Sieber, B. Qu, Y.
Xu, Z. Li, J. T. Reeves, J. N. Desrosiers, S. Ma, N. Grinberg,
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Exemplar: Reaction with Methyl(phenyl)(o-tolyl)phosphane Oxide
(oxo-1a): Oxalyl chloride neat (0.10 mL, 1.2 mmol, 1.2 equiv.) was
added dropwise at room temperature to a solution of phosphane
oxide (0.25 g, 1.0 mmol, 1.2 equiv.) in 7.0 mL of dry DCM in
25 mL Young’s tube and the reaction was allowed to stir for 2 h.
A sample of 0.1 mL of the mixture was added to 0.60 mL of CDCl3
for 31P-NMR to confirm full conversion of phosphane oxide to
CPS. DCM and excess oxalyl chloride were completely removed
through a dedicated cold trap connected to Schlenk manifold until
the syrupy residue forms light off-white foam. 4.0 mL of dry DCM
was added to the reaction mixture to dissolve CPS again. The reac-
tion mixture was cooled to –82 °C using ethyl acetate/N2 mixture
and (–)-menthol stock solution (11.7 mL, 1.6 mmol, 0.137 m,
1.6 equiv.) was added in dry toluene dropwise to the reaction mix-
ture. The reaction was maintained at –82 °C for 3 h and then
warmed to 0 °C and kept in an ice bath. Sampling of DAPS for
31P-NMR was then performed (see ref.[13]).
Then the solvent was completely removed from the reaction mix-
ture in the flask under vacuum at 0 °C. The residue was dissolved
in dry DCM (3 mL) and was cooled to –82 °C. LiBH4 in THF
(0.75 mL, 1.5 mmol, 5 equiv.) was added dropwise through a sy-
ringe. The reaction mixture was stirred under nitrogen –82 °C to
room temperature overnight. The reaction mixture was cooled to
0 °C and quenched with HCl solution 1 m in deionized water. The
aqueous layer was extracted with DCM (2ϫ 5 mL) and the com-
bined organic layers were washed with deionized water (3ϫ 5 mL),
dried with anhydrous MgSO4. The drying agent was removed by
filtration, and the solvent was removed in vacuo. The crude product
was purified by column chromatography on silica gel ethyl acetate/
cyclohexane (6:94) yielding the phosphane–borane as a colourless
oil (0.2 g, 88%). HPLC and NMR analysis as above [CHI-
RALPAK® ASH column, (98:2), heptane/EtOH, 1.0 mL/min: 84%
ee, Rt = 9.5, 11.7 min].
Similar procedures were followed to generate other scalemic phos-
phane–boranes 6b-7b from the corresponding oxo-6a, oxo-7a, (see
Supporting Information). The same procedure but excluding the
hydride reduction was performed for oxo-8a–oxo10a.
Supporting Information (see footnote on the first page of this arti-
cle): Examplar 1H, 31P spectra of phosphane, phosphane oxide,
CPS and phosphane–boranes. 31P-NMR spectra of all DAPS spe-
cies and HPLC chromatograms for all product phosphane–bor-
anes. Characterisation of phosphane oxide 10a and boranes 8b/9b.
[3] For reviews on P-stereogenic compounds, see: a) A. Grabulosa,
J. Granell, G. Muller, Coord. Chem. Rev. 2007, 251, 25–90; b)
D. S. Glueck, Synlett 2007, 2627–2634; c) M. J. Johansson,
N. C. Kann, Mini-Rev. Org. Chem. 2004, 1, 233–247; d) K. M.
Pietrusiewicz, M. Zablocka, Chem. Rev. 1994, 94, 1375–1411;
A. Grabulosa (Ed.), P-Stereogenic Ligands in Enantioselective
Catalysis, Royal Society of Chemistry, Cambridge, UK, 2011;
O. I. Kolodiazhnyi, Tetrahedron: Asymmetry 2012, 23, 1–46.
[4] a) E. Bergin, C. T. O’Connor, S. B. Robinson, E. M. McGarri-
gle, C. P. O’Mahony, D. G. Gilheany, J. Am. Chem. Soc. 2007,
129, 9566–9567; b) G. King, E. Bergin, H. Müller-Bunz, D. G.
Acknowledgments
The authors sincerely thank Science Foundation Ireland (SFI)
for funding this chemistry under grants RFP/08/CHE1251 and
5964
www.eurjoc.org
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Eur. J. Org. Chem. 2015, 5959–5965