Copper-Catalyzed Insertions of Silacyclopropanes
J. Am. Chem. Soc., Vol. 121, No. 5, 1999 955
126.6, 96.2, 58.4, 45.4, 34.9, 27.9, 27.7, 27.6, 22.2, 20.9, 20.3, 16.1,
4.5. IR (thin film): 2958, 2857, 1471, 1365, 1011 cm-1. HRMS (GC-
MS, electron ionization (EI)): m/z calcd for C22H39NOSi (M+),
361.2801; found, 361.2803.
insertion was followed using silacyclopropane 8 (0.118 g, 0.555 mmol),
CuBr2 (0.009 g, 0.040 mmol), and 2-methyl-2-butenal (0.180 mL, 2.14
mmol). After extraction, GC analysis of the unpurified product showed
a pair of diastereomers (10c) in a ratio of 99:1. The resulting oil was
purified by flash chromatography (5:95-12:88 CH2Cl2/hexanes) to yield
the product as a clear oil (0.123 g, 75%) as an inseparable mixture of
diastereomers. The resonances for each isomer were identifiable in the
spectra.21 Combustion analysis and IR data were obtained for the
mixture of diastereomers. IR (thin film): 2960, 1472, 1365, 1068, 982
cm-1. Anal. Calcd for C18H36OSi: C, 72.90; H, 12.24. Found: C, 72.82;
H, 12.26.
4-Isopropyl-5-phenyl-2-di-tert-butyl-1-oxa-2-silacyclopentane (10a).
Representative Procedure for Copper-Catalyzed Insertion. To a
cooled (-78 °C) solution of silacyclopropane 8 (0.200 g, 0.937 mmol)
in 8 mL of CH2Cl2 were added CuBr2 (0.023 g, 0.102 mmol) and
benzaldehyde (0.300 mL, 2.82 mmol). The mixture was allowed to
warm to 22 °C and was stirred for 12 h, and then 5 mL of MeOH was
added. The mixture was treated with 10 mL of sodium potassium tartrate
(saturated aqueous), and the aqueous layer was extracted with 3 × 10
mL of CH2Cl2. The combined organic layers were washed with 10 mL
of brine, dried (Na2SO4), and concentrated in vacuo. After extraction,
GC analysis of the unpurified product showed a pair of diastereomers
in a ratio of 91:9 as well as product 11. Purification by flash
chromatography (0:100-10:90 CH2Cl2/hexanes) yielded 11 (0.020 g,
7%) and a mixture of diastereomers 10a as colorless oil. The mixture
of diastereomers solidified over several days (0.246 g, 82%). Combus-
tion analysis and IR data were obtained for 10a as a mixture of
1
10c. H NMR (500 MHz, CDCl3): δ 5.49 (m, 1H), 3.95 (d, J )
10.8, 1H), 1.83 (m, 1H), 1.66 (d, J ) 6.2, 3H + m, 1H) 1.65 (s, 3H),
1.08 (s, 9H), 1.06 (s, 9H), 0.93 (d, J ) 6.9, 3H), 0.81 (d, J ) 6.7, 3H),
0.73 (dd, J ) 14.6, 7.4, 1H), 0.65 (dd, J ) 14.6, 12.5, 1H). 13C NMR
(125 MHz, CDCl3): δ 136.1, 123.4, 87.6, 46.6, 27.8, 27.7, 27.2, 22.4,
21.0, 20.1, 15.5, 13.3, 10.1, 4.9. HRMS (GC-MS, EI): m/z calcd for
C18H36OSi (M+), 296.2535; found, 296.2544.
Minor cis Isomer of 10c. 1H NMR (500 MHz, CDCl3, not all signals
were sufficiently resolved): δ 5.53 (m, 1H), 4.60 (d, J ) 8.4, 1H),
1.67 (s, 3H), 1.61 (d, J ) 6.7, 3H), 1.51 (m, 1H), 1.09 (s, 9H), 1.07 (s,
9H), 0.97 (d, J ) 6.6, 3H), 0.88 (d, J ) 6.3, 3H). 13C NMR (125 MHz,
CDCl3): δ 136.1, 124.0, 86.9, 49.4, 30.7, 28.9, 28.4, 22.8, 22.7, 21.4,
20.2, 14.9, 13.1, 11.4. HRMS (GC-MS, EI): m/z calcd for C18H36OSi
(M+), 296.2535; found, 296.2535.
diastereomers. IR (thin film): 3030, 1471, 1386, 1068, 1019 cm-1
.
Anal. Calcd for C20H34OSi: C, 73.95; H, 11.76. Found: C, 73.89; H,
11.72. The resonances for each diastereomer were identifiable in the
spectra.
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10a. H NMR (500 MHz, CDCl3): δ 7.29 (m, 5H), 4.52 (d, J )
10.7, 1 H), 1.84 (m, 1H), 1.58 (m, 1H), 1.14 (s, 9H), 1.07 (s, 9H), 0.89
(d, J ) 6.7, 3H), 0.81 (d, J ) 6.8, 3H), 0.78 (m, 2H). 13C NMR (125
MHz, CDCl3): δ 143.7, 128.2, 127.4, 126.6, 83.3, 53.3, 27.8, 27.7,
26.5, 22.5, 21.1, 20.3, 15.5, 5.3. HRMS (GC-MS, EI): m/z calcd for
C20H33OSi (M - H)+, 317.2301; found, 317.2302.
Oxasilacyclopentane 10d. The representative procedure for copper-
catalyzed insertion was followed using silacyclopropane 8 (0.228 g,
1.07 mmol), CuI (0.019 g, 0.10 mmol), and 2-cyclohexene-1-one (0.350
mL, 3.64 mmol). After extraction, GC analysis of the unpurified product
showed a pair of diastereomers (10d) in a ratio of 65:35. The resulting
oil was purified by flash chromatography (5:95-10:90 CH2Cl2/hexanes)
to yield each diastereomer of product as a clear oil (0.197 g, 60%
combined). Combustion analysis and IR data were obtained for products
10d as a mixture of diastereomers. IR (thin film): 3036, 1473, 1384,
1082, 958 cm-1. Anal. Calcd for C19H36OSi: C, 75.40; H, 10.76.
Found: C, 75.49; H, 10.79.
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Minor cis Isomer of 10a. H NMR (500 MHz, CDCl3, distinctive
peaks): δ 7.29 (m, 5H), 5.18 (d, J ) 8.3, 1H), 2.29 (m, 1H), 1.53 (m,
1H), 1.09 (s, 9H), 1.00 (s, 9H). 13C NMR (125 MHz, CDCl3): δ 141.6,
129.3, 127.6, 127.2, 83.5, 51.2, 31.4, 28.7, 28.4, 22.3, 21.7, 21.2, 20.0,
11.2. HRMS (GC-MS, EI): m/z calcd for C20H33OSi (M - H)+,
317.2301; found, 317.2299.
1-(Benzyloxy)-1-[2-(3-methyl-1-butenyl)]di-tert-butylsilane (11).
1H NMR (500 MHz, CDCl3): δ 7.35 (m, 4H), 7.25 (m, 1H), 5.82 (dd,
J ) 1.7, 0.9, 1H), 5.49 (d, J ) 2.0, 1H), 5.02 (s, 1H), 2.59 (m, 1H),
1.09 (s, 18H), 1.06 (d, J ) 6.8, 6H). 13C NMR (125 MHz, CDCl3): δ
155.2, 141.6, 128.2, 126.7, 125.6, 124.4, 66.2, 31.3, 28.7, 23.5, 21.4.
HRMS (EI): m/z calcd for C20H34OSi (M - C4H9)+, 261.1675; found,
261.1670.
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10d. H NMR (500 MHz, CDCl3): δ 5.72 (m, 1H), 5.64 (d, J )
10.1, 1H), 2.03 (m, 1H), 1.89 (m, 2H), 1.79 (m, 1H), 1.69 (m, 1H),
1.56 (m, 3H), 1.01 (s, 9H), 1.00 (s, 9H), 0.98 (m, 1H), 0.93 (d, J )
6.3, 3H), 0.90 (d, J ) 6.5, 3H), 0.61 (dd, J ) 14.9, 12.7, 1H). 13C
NMR (125 MHz, CDCl3): δ 130.3, 127.9, 79.9, 54.3, 38.2, 31.0, 29.7,
28.4, 28.1, 25.2, 23.8, 22.0, 19.7, 19.7, 10.0. HRMS (CI/isobutane):
m/z calcd for C19H36OSi (M+), 308.2535; found, 308.2528.
4-Isopropyl-5-(1-propenyl)-2-di-tert-butyl-1-oxa-2-silacyclopen-
tane (10b). The representative procedure for copper-catalyzed insertion
was followed using silacyclopropane 8 (0.070 g, 0.35 mmol), CuBr2
(0.008 g, 0.035 mmol), and crotonaldehyde (0.100 mL, 1.21 mmol).
After extraction, GC analysis of the unpurified product showed a pair
of diastereomers (10b) in a ratio of 98:2. The resulting oil was purified
by flash chromatography (5:95-15:85 CH2Cl2/hexanes) to yield the
major diastereomer and an enriched sample of the minor diastereomer
(0.074 g, 74% combined).21 Combustion analysis and IR data were
obtained for the mixture of diastereomers. IR (thin film): 2958, 1471,
1365, 1068, 1000. Anal. Calcd for C17H34OSi: C, 72.27; H, 12.13.
Found: C, 72.00; H, 12.11.
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Minor Isomer of 10d. H NMR (500 MHz, CDCl3): δ 5.74 (m,
1H), 5.58 (dd, J ) 11.0, 1.0, 1 H), 2.11 (m, 1H), 1.93 (m, 1H), 1.86
(m, 1H), 1.70 (m, 1H), 1.64 (m, 1H), 1.60 (m, 2H), 1.52 (m, 2H), 1.03
(s, 9H + m, 1H), 1.02 (s, 9H), 0.96 (d, J ) 6.5, 3H), 0.87 (d, J ) 6.5,
3H), 0.57 (t, J ) 14.1, 1H). 13C NMR (125 MHz, CDCl3): δ 136.2,
128.8, 79.7, 55.6, 31.3, 30.2, 28.7, 28.5, 25.5, 22.9, 22.7, 20.5, 19.7,
18.2, 11.1. HRMS (CI/isobutane): m/z calcd for C19H36OSi (M+),
308.2535; found, 308.2526.
4-Isopropyl-5-methyl-5-(2-methyl-1-propenyl)-2-di-tert-butyl-1-
oxa-2-silacyclopentane (10e). The representative procedure for copper-
catalyzed insertion was followed using silacyclopropane 8 (0.124 g,
0.584 mmol), CuBr2 (0.010 g, 0.044 mmol), and mesityl oxide (0.200
mL, 1.75 mmol). After extraction, analysis of the unpurified product
1
10b. H NMR (500 MHz, CDCl3): δ 5.66 (m, 1H), 5.40 (dd, J )
15.2, 7.8, 1H), 3.93 (dd, J ) 10.2, 8.0, 1H), 1.75 (m, 1H), 1.71 (d, J
) 6.5, 3H), 1.61 (m, 1H), 1.02 (s, 18H), 0.91 (d, J ) 6.9, 3H), 0.79 (d,
J ) 6.8, 3H), 0.69 (dd, J ) 14.7, 7.9, 1H), 0.61 (dd, J ) 14.6, 12.5,
1H). 13C NMR (125 MHz, CDCl3): δ 133.8, 127.7, 82.6, 50.4, 27.8,
27.6, 27.3, 22.6, 20.8, 19.9, 17.8, 15.8, 5.0. HRMS (GC-MS, EI):
m/z calcd for C17H34OSi (M+), 282.2379; found, 282.2376.
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by H NMR spectroscopy showed a pair of diastereomers (10e) in a
ratio of 62:38. The resulting oil was purified by flash chromatography
(95.5:0.5 hexanes/Et3N) to yield the products as a clear oil (0.142 g,
78% combined). Analytical data were obtained for products 10e as a
mixture of diastereomers. IR (thin film): 2931, 2857, 1474, 1370, 1105
cm-1. Anal. Calcd for C19H38OSi: C, 73.47; H, 12.33. Found: C, 73.29;
H, 12.25.
Minor cis Isomer of 10b. 1H NMR (500 MHz, CDCl3): δ 5.68 (m,
1H), 5.46 (m, 1H), 4.53 (dd, J ) 9.9, 7.2, 1H), 1.83 (m, 1H), 1.69 (dd,
J ) 6.5, 1.6, 3H), 1.60 (m, 1H), 1.32 (m, 1H), 1.04 (s, 9H), 1.02 (s,
9H), 0.95 (d, J ) 6.7, 3H), 0.83 (d, J ) 6.4, 3H), 0.47 (t, J ) 14.1,
1H). 13C NMR (125 MHz, CDCl3): δ 130.0, 128.7, 82.3, 49.6, 31.0,
29.7, 28.6, 28.1, 22.4, 21.1, 19.6, 17.8, 10.0. HRMS (GC-MS, EI):
m/z calcd for C17H34OSi (M+), 282.2379; found, 282.2381.
1
10e. H NMR (500 MHz, CDCl3): δ 5.34 (dd, J ) 1.5, 1.0, 1H),
1.86 (d, J ) 1.5, 3H), 1.74 (m, 1H), 1.68 (d, J ) 1.0, 3H), 1.60 (m,
1H), 1.25 (s, 3H), 1.03 (s, 9H), 0.98 (s, 9H), 0.95 (d, J ) 6.5, 6H),
0.83 (m, 1H), 0.48 (m, 1H). 13C NMR (125 MHz, CDCl3): δ 132.8,
131.5, 83.2, 55.6, 30.8, 28.6, 28.1, 27.9, 24.4, 23.7, 21.9, 20.6, 19.7,
19.1, 8.9. HRMS (CI/isobutane): m/z calcd for C19H38OSi (M+),
310.2692; found, 310.2696.
4-Isopropyl-5-(1-methyl-1-propene)-2-di-tert-butyl-1-oxa-2-sila-
cyclopentane (10c). The representative procedure for copper-catalyzed