J. Drabowicz et al. / Tetrahedron: Asymmetry 10 (1999) 2757–2763
2761
4. Experimental
4.1. General
NMR spectra were recorded on a Bruker AC 200 spectrometer at 200 MHz. All optical rotation
measurements were done on a Perkin–Elmer MC 241 photopolarimeter. Reactions were monitored by
TLC chromatography (Merck Kieselgel 60 F254). Column chromatography was conducted on Merck
silica gel (70–230 mesh).
0
4
.2. Resolution of racemic t-butylphenylphosphine oxide 1 with enantiomerically pure (+)-1,1 -bi-
0
naphthalene-2,2 -diol 4
A heterogeneous mixture of racemic t-butylphenylphosphine oxide 1 (0.1472 g, 0.8 mmol) and (+)-
(R)-4 (0.116 g, 0.4 mmol) in 3.5 ml of water was stirred at room temperature for 15 h. The white crystals
formed were separated by filtration. The isolated complex of the phosphine oxide 1 and the binaphthol
2
5
1
4
(0.152 g, ∼50% yield) had [α] =−19.7 (c=1.14, CHCl ) and the following spectroscopic data: H
5
89
3
31
NMR (CDCl ) δ=1.123 (d, J=16.72 Hz, 9H); 5.83 (bs, 3H); 7.00–8.00 (m, 17H); P NMR (CDCl3)
3
δ 48.64 (s). Column chromatography of this complex (0.09 g) on silica gel (5 g) gave after elution
with a 1:1 mixture of ethyl ether and petroleum ether enantiomerically pure (+)-(R)-4. Further elution
2
5
with chloroform afforded optically active t-butylphenylphosphine oxide (−)-1 (0.030 g): [α] =−21.5
5
89
1
31
(
c=1.18, CHCl ); ee=58%. The H and P NMR spectral data fully supported its structure. In order
3
to isolate the non-complexed phosphine oxide 1, the water phase was extracted with chloroform (3×5
ml). The chloroform solution was dried over anhydrous magnesium sulfate. Evaporation of the solvent in
vacuo gave the analytically pure phosphine oxide (+)-1 [(0.068 g, 45%); [α]2 =+22.2 (c=1.34, CHCl );
5
5
89
3
ee=59.7%].
Repetition of the resolution procedure of this sample of (+)-1 using 0.05 g of (+)-(R)-4 gave, after
extraction from the water phase, the non-complexed phosphine oxide (+)-1 (0.0448 g) with [α]2 =+28.6
5
5
89
(
c=2.24, CHCl ); ee=77%.
3
4.3. Resolution of racemic t-butylphenylphosphine oxide 1 with enantiomerically pure (+)-(S)-mandelic
acid 5
Racemic t-butylphenylphosphine oxide 1 (1.84 g, 0.01 mol) was dissolved in ethyl ether (10 ml).
Compound (+)-(S)-5 (1.52 g, 0.01 mol) was added slowly to this solution. After addition of each portion
the solid acid disappeared rapidly. A few minutes after the addition of the last portion of the acid the
colourless crystals of the complex started to appear. The reaction mixture was left at room temperature
2
5
for 72 h. The complex formed was filtered off (1.01 g, 33.9%). It had [α]5 =+70.2 (c=2.14, CHCl3)
89
1
and the following spectroscopic data: H NMR (CDCl ) δ=1.116 (d, J=16.97 Hz, 9H); 5.153 (s, 1H);
3
1
7
.01 (d, J=463.74 Hz, 1H); 7.25–7.75 (m, 10H); 31P (CDCl ) δ=49.77 (s). The H NMR data indicated
3
that the isolated complex contained only a single diastereoisomer. In order to isolate enantiomerically
pure t-butylphenylphosphine oxide, the isolated complex (500 mg) was dissolved in 4 ml of 5% aqueous
solution of K CO and the water phase was extracted with CHCl (4×5 ml). The combined chloroform
2
3
3
solutions were dried over anhydrous magnesium sulfate. Evaporation of the solvent gave the virtually
2
5
pure t-butylphenylphosphine oxide (−)-1 (0.261 g, 28.4%) with [α] =−40.45 (c=1.78, MeOH) and
5
89
2
5
1
31
[
α]5 =−36.6 (c=1.38, CHCl ). The spectral and analytical data ( H, P and HRMS) fully supported
89
3
25
its structure. Evaporation of the mother liquor gave an oil (2.190 g, 65.2%) with [α]5 =+91.55 (c=3.1
89