Q. Wang et al. / Tetrahedron: Asymmetry 9 (1998) 3971–3977
3975
13
Hz, Ph), 4.69 (s, 5H, C H ), 3.70 (s, 3H, OCH ), 0.28 (s, 9H, Si(CH ) ); C NMR (CDCl , 250 MHz)
5
5
3
3 3
3
δ: 234.6 (Cr(CO) ), 216.7, 215.2 (Fe(CO) ), 135.2 (COCH ), 120.1, 92.1, 89.5, 86.7 (C H ), 85.7, 84.9,
3
2
3
5
5
−1
7
3.7 (FeCH), 54.8 (OCH ), 0.47 (Si(CH ) ). IR (CH Cl ) ν : 2007, 1953, 1872 cm . Anal. calcd for
FeC H O CrSi: C, 48.29; H, 4.24. Found: C, 48.12; H, 4.21. [α]
3
3 3
2
2
CO
20
−335 (c, 0.226, CHCl3).
21
22
7
D
3.2. SS-(−)-2,2-Dimethyl-1-O-methoxyphenyl(tricarbonyl chromium)cyclopropane (−)-8
A 2.5–3.0 mmol (1 equiv.) sample of the bimetallic complex (−)-6 was dissolved in 25 ml of CH Cl
2
2
and cooled to −78°C, and an excess of 2-methylpropene, which had been condensed to liquid at −78°C,
was introduced. After adding 3.0–3.6 mmol (1.1 equiv.) of trimethylsilyl triflate, the solution was stirred
for 4 h at −78°C and warmed to room temperature over 0.5 h. The color of the reaction mixture changed
to purple after several minutes of stirring. After the treatment of the reaction mixture with a short-wash
column of neutral alumina (activity IV) under nitrogen, the solvent was removed under reduced pressure.
The crude product was then separated with a chromatography column on neutral alumina (activity IV)
1
and a bright yellow solid of (−)-8 was isolated in 91% yield. H NMR (CDCl , 250 MHz) δ: 5.36–5.42
3
(
m, 2H, Ph), 5.13 (d, 1H, J=6.6 Hz, Ph), 4.90 (t, 1H, J=6.2 Hz, Ph), 3.77 (s, 3H, OCH ), 1.85 (t, 1H,
3
J=7.2 Hz, CH), 1.19 (s, 3H, CH ), 0.82 (s, 3H, CH ), 0.81 (t, 1H, J=5.4 Hz, CH ), 0.64 (t, 1H, J=5.5
3
3
2
1
3
Hz, CH2); C NMR (CDCl , 250 MHz) δ: 232.4 (Cr(CO) ), 163.9, 142.2, 95.7, 92.7, 85.8, 74.8 (Ph),
6.0 (OCH ), 26.7, 19.8, 20.2 (cyclopropane), 24.8 (CH ), 18.2 (CH ). Anal. calcd for C H O Cr: C,
7.69; H, 5.16. Found: C, 57.74; H, 5.25. m/z: 312 (22%, M ). [α]D −191 (c, 0.273, CHCl3).
3
3
5
5
3
3
3
20
15 16
4
+
3.3. S-(−)-2,2-Dimethyl-1-O-methoxyphenylcyclopropane (−)-9
A 2.2–2.8 mmol sample of (−)-8 was dissolved in 200–250 ml solvent (pentane:ether, 50:50), and
stirred under a sun lamp or natural sunlight for 3 days while air was bubbled through the solution. The
solution became colorless. After gravity filtration, the solvent was removed by a rotavapor and a clear oil
of (−)-9 was obtained in 97% yield. The enantiomeric excess of the product was determined by adding
1
4
0 mg of Yb(hfc) into 4 mg of (−)-9 in 0.5 ml CDCl and the split peaks of the methoxy proton in H
3
3
1
NMR spectrum were used to determine the ee of (−)-9. A >95% ee of (−)-9 was indicated. H NMR
(
6
(
1
CDCl , 250 MHz) δ: 7.16 (t, 1H, J=7.7 Hz, Ph), 7.01 (d, 1H, J=6.4 Hz, Ph), 6.86 (t, 1H, J=7.4 Hz, Ph),
3
.83 (d, 1H, J=8.0 Hz, Ph), 3.83 (s, 3H, OCH ), 1.83 (t, 1H, J=7.3 Hz, CH), 1.24 (s, 3H, CH ), 0.75
3
3
13
d, 2H, J=7.3 Hz, CH ), 0.70 (s, 3H, CH ); C NMR (CDCl , 250 MHz) δ: 159.7, 129.4, 129.0, 126.7,
20.1, 110.0 (Ph), 55.5 (OCH ), 27.1 (CH ), 25.6 (CH), 20.1 (C(CH ) ), 18.2 (CH ), 17.8 (CH ). Anal.
calcd for C H O: C, 81.77; H, 9.15. Found: C, 81.80; H, 9.46. m/z: 176 (46%, M ), 161 (94, M−Me)
2
3
3
3 2 3 2 3 3
+
12
16
20
and 146 (16, M−2Me). [α]D −51 (c, 0.548, CHCl ).
3
3.4. S-(+)-2,2-Dimethylcyclopropane carboxylic acid (+)-10
A 2.0–2.5 mmol sample of (−)-9 was dissolved in 60 ml of CH Cl and cooled to −78°C, and a stream
2
2
of ozone was bubbled through the solution for 0.5 h. Bubbling was continued for 8 h, and the temperature
was maintained at −20 to −30°C. The reaction mixture was then poured into a solution of 20 ml 30%
H O in 60 ml 10% NaOH, and stirred overnight at room temperature. After acidifying the solution to pH
2
2
3
, the reaction mixture was extracted with CH Cl , and dried over MgSO . After fractional distillation
2 2 4
the final product of S-(+)-2,2-dimethylcyclopropane carboxylic acid (+)-10 was obtained in 82% yield.
1
H NMR (CDCl , 250 MHz) δ: 1.51 (dd, 1H), 1.24 (s, 3H), 1.15 (s, 3H), 1.11 (dd, 1H), 0.93 (dd, 1H);
3