1000
M. Nour et al. / Tetrahedron: Asymmetry 11 (2000) 995–1002
dried over anhydrous MgSO4. Chemicals obtained from commercial suppliers were used without further
purification. All elemental analyses were performed by the Service de microanalyse, Centre d’Etudes
Pharmaceutiques, Châtenay-Malabry, France, with a Perkin–Elmer 2400 analyzer.
3.2. (S)-(1-Phenylethyl)-(2-phenylsulfenylcyclohex-1-enyl)amine 7
A solution of 2-phenylthiocyclohexanone 6 (0.93 g, 4.5 mmol), (S)-1-phenylethylamine 2 (0.55 g, 4.5
mmol) and p-toluenesulfonic acid (10 mg) in anhydrous toluene (80 mL) was refluxed for 12 h with
azeotropic removal of water. The solution was cooled to 20°C and the solvent was removed in vacuo to
1
afford the crude enamine 7 as a yellow oil; IR (film, cm−1) 3300, 1618, 1581; H NMR (CDCl3, 200
MHz) δ: 7.45–6.85 (m, 10H), 5.5 (d, J=7.0 Hz, 1H), 4.2 (quint., J=7.0 Hz, 1H), 2.35–1.60 (m, 4H),
1.40–1.20 (m, 4H), 1.05 (d, J=7.0 Hz, 3H).
3.3. (S)-3-(2-Oxo-1-phenylsulfenylcyclohexyl)propionic acid methyl ester 8
To the enamine 7 (0.31 g, 1.0 mmol) were added freshly distilled methyl acrylate (1.0 g, 12 mmol),
hydroquinone (5 mg) and THF (20 mL). The stirred mixture was heated at 20°C for 24 h and 5 mL of
20% aqueous acetic acid were added. The mixture was stirred for 3 h. The solvents were removed under
reduced pressure and 1N hydrochloric acid (10 mL) was added. The mixture was extracted with ether
and the combined organic phases were washed with brine, dried and concentrated. Chromatographic
purification over silica gel (1:1 hexane:dichloromethane) gave keto ester 8 (199 mg, 68%) as a colorless
1
oil; [α]D20=−195 (c 1.0, MeOH); IR (film, cm−1) 1735, 1705, 1438; H NMR (CDCl3, 200 MHz) δ:
7.30–7.10 (m, 5H), 3.56 (s, 3H), 3.25 (ddd, J=14.5, 13.2, 6.2 Hz, 1H), 2.55–2.15 (m, 3H), 2.05–1.50 (m,
8H); 13C NMR (CDCl3, 50 MHz) δ: 206.9 (C), 173.8 (C), 136.2 (2 CH), 129.8 (C), 129.5 (CH), 129.0
(2 CH), 60.9 (C), 51.6 (CH3), 37.8 (CH2), 36.4 (CH2), 29.8 (CH2), 28.8 (CH2), 26.9 (CH2), 21.2 (CH2);
anal. calcd: C, 65.72: H, 6.89; found: C, 64.98: H, 6.75.
3.4. (S)-2-(3-Oxobutyl)-2-phenylsulfenylcyclohexanone 9
To the enamine 7 (0.155 g, 0.5 mmol) were added at 0°C freshly distilled methyl vinyl ketone (1.0
g, 15 mmol), hydroquinone (3 mg) and THF (10 mL). The stirred mixture was kept at 0°C for 12
h and 5 mL of 10% aqueous acetic acid were added. The mixture was stirred for 1 h. The solvents
were removed under reduced pressure and 1N hydrochloric acid (10 mL) was added. The mixture was
extracted with dichloromethane and the combined organic phases were washed with brine, dried and
concentrated. Chromatographic purification over silica gel (1:1 hexane:dichloromethane) gave adduct
9 (83 mg, 60%) as colorless crystals; mp 62–63°C (hexane); [α]D20=−187 (c 2.0, MeOH); IR (film,
1
cm−1) 1717, 1700, 1438; H NMR (CDCl3, 200 MHz) δ: 7.30–7.10 (m, 5H), 3.35 (ddd, J=14.0, 13.3,
6.1 Hz, 1H), 2.60–2.30 (m, 3H), 2.05 (s, 3H), 2.00–1.50 (m, 8H); 13C NMR (CDCl3, 50 MHz) δ: 207.8
(C), 207.0 (C), 136.0 (2 CH), 129.8 (C), 129.3 (CH), 128.8 (2 CH), 61.0 (C), 38.1 (CH2), 37.8 (CH2),
36.6 (CH2), 29.8 (CH2), 28.4 (CH2), 26.7 (CH2), 21.1 (CH3); anal. calcd: C, 69.53; H, 7.29; found: C,
69.48; H, 7.42. Crystal data: C16H20O2S, Mw=276.38, crystal of 0.40×0.10×0.02 mm, orthorhombic,
space group P 21 21 21, Z=8, a=6.927(3), b=12.778(6), c=35.064(8) Å, V=3103.6(21) Å3, dcalc=1.183
g cm−3, F(000)=1184, λ=1.54180 Å (CuKα), µ=1.812 mm−1, Nonius CAD4 diffractometer, theta
range: 2.52–67.87°, 3484 collected reflections, 3051 unique (Rint=0.0446), 1328 observed ( I>2σ(I)),
full-matrix least-squares (SHELXL93), R=0.0529 for 1328 observed reflections, wR2=0.1304 for 3051
unique reflections, goodness of fit=0.944, residual electron density between −0.233 and 0.207 eA−3
,