8128 J. Am. Chem. Soc., Vol. 122, No. 34, 2000
Nakamura et al.
Preparation of R-Arylcarboxylic Acids 6a-i. 2-Chloro-2-(4-bro-
mophenyl)acetic acid (6i) was produced with a simple method reported
previously.29 Other 2-arylcarboxylic acids 6a-h were purchased.
Preparation of Ketene Bis(trialkylsilyl) Acetals 5a-e.12a-c To a
solution of LDA (20 mmol) in THF (15 mL) was added a solution of
the carboxylic acid (10 mmol) in THF (50 mL) dropwise with stirring
at 0 °C, which was continued at 0 °C for a further 0.5 h. Excess
trialkylsilyl chloride (50 mmol) was added dropwise over 5 min, and
the reaction mixture was allowed to come to ambient temperature over
2 h with stirring. It was then filtered by suction through a pad of Celite,
and concentrated using a rotary evaporator. The residue was taken up
in ether (5 mL), and filtration and concentration were repeated.
Distillation in vacuo of the residue gave the ketene bis(trialkylsilyl)
acetals, ca. 90%.
the reaction mixture was allowed to come to ambient temperature over
5 h with stirring. It was then filtered by suction through a pad of Celite,
and concentrated using a rotary evaporator. The residue was taken up
in ether (5 mL), and filtration and concentration were repeated.
Distillation in vacuo (0.4 Torr) of the residue gave the ketene bis-
(trimethylsilyl) acetals, ca. 90%.
1,1-Bis(trimethylsilyloxy)-2-fluoro-2-phenylethene (5f): IR (film)
2961, 1676, 1283, 1256, 1136, 1042, 922, 847, 758, 692 cm-1; 1H NMR
(CDCl3, 300 MHz) δ 0.27 (s, 9H, Si(CH3)3), 0.30 (d, J ) 1.8 Hz, 9H,
Si(CH3)3), 7.12 (t, J ) 7.5 Hz, 1H, ArH), 7.31 (t, J ) 7.5 Hz, 2H,
ArH), 7.54 (d, J ) 7.5 Hz, 2H, ArH); 13C NMR (CDCl3, 75 MHz) δ
0.47, 0.57 (d, J ) 3.8 Hz), 30.47 (d, J ) 113.3 Hz), 89.63 (d, J )
186.1 Hz), 122.86 (d, J ) 7.7 Hz), 124.99, 127.97 (d, J ) 2.6 Hz),
142.98 (d, J ) 41.0 Hz); 19F NMR (CDCl3, 282 MHz) δ -171.61 (s).
1,1-Bis(trimethylsilyloxy)-2-chloro-2-phenylethene (5g): IR (film)
The physical properties and analytical data of the ketene disilyl
acetals thus obtained are listed below.
2961, 1644, 1254, 1051, 920, 945, 847, 758, 695 cm-1 1H NMR
;
1,1-Bis(trimethylsilyloxy)-2-phenylpropene (5a):12b IR (film) 2961,
(CDCl3, 300 MHz) δ 0.05 (s, 9H, Si(CH3)3), 0.34 (s, 9H, Si(CH3)3),
7.15 (t, J ) 7.5 Hz, 1H, ArH), 7.28 (t, J ) 7.5 Hz, 2H, ArH), 7.56 (d,
J ) 7.5 Hz, 2H, ArH); 13C NMR (CDCl3, 75 MHz) δ 0.06, 0.54, 96.71,
126.12, 127.60, 128.44, 136.87, 148.43.
1,1-Bis(trimethylsilyloxy)-2-bromo-2-phenylethene (5h): IR (film)
2961, 1640, 1266, 1254, 1049, 1028, 928, 847, 756, 695 cm-1; 1H NMR
(CDCl3, 300 MHz) δ 0.01 (s, 9H, Si(CH3)3), 0.37 (s, 9H, Si(CH3)3),
7.15 (t, J ) 7.5 Hz, 1H, ArH), 7.27 (t, J ) 7.5 Hz, 2H, ArH), 7.51 (d,
J ) 7.5 Hz, 2H, ArH); 13C NMR (CDCl3, 75 MHz) δ -0.07, 0.46,
86.19, 126.43, 127.62, 129.86, 138.12, 158.87.
1
1655 (CdC) 1254, 1213, 1140, 1069, 963, 851, 756, 698 cm-1; H
NMR (CDCl3, 300 MHz) δ -0.05 (s, 9H, Si(CH3)3), 0.27 (s, 9H, Si-
(CH3)3), 1.90 (s, 3H, CdCCH3), 7.07 (tt, J ) 2.6, 7.2 Hz, 1H, ArH),
7.20-7.38 (m, 4H, ArH); 13C NMR (CDCl3, 75 MHz) δ 0.05, 0.42,
16.51, 94.48, 124.73, 127.53, 128.57, 141.62, 147.28; LR FAB+-MS
m/z 294 ([M]+, C15H26O2Si2 requires 294.5).
1,1-Bis(triethylsilyloxy)-2-phenylpropene (5a): IR (film) 2957,
2878, 1655 (CdC), 1458, 1414, 1208, 1140, 1005, 816, 760 cm-1 1 H
;
NMR (CDCl3, 300 MHz) δ 0.39 (q, J ) 8.0 Hz, 6H, Si(CH2CH3)3),
0.77 (q, J ) 7.8 Hz, 6H, Si(CH2CH3)3), 0.80 (t, J ) 8.0 Hz, 9H, Si-
(CH2CH3)3), 1.04 (t, J ) 7.8 Hz, 9H, Si(CH2CH3)3), 1.90 (s, 3H,
CH3CdC), 7.04-7.35 (m, 5H, C6H5); 13C NMR (CDCl3, 75 MHz) δ
4.69, 5.17, 6.44, 6.65, 16.73, 93.89, 124.66, 127.50, 128.72, 141.88,
147.72; LR FAB+-MS m/z 342 ([M]+, C18H38O2Si2 requires 342.7).
1,1-Bis(trimethylsilyloxy)-2-phenylbutene (5b): IR (film) 2961,
1,1-Bis(trimethylsilyloxy)-2-chloro-2-(4-bromophenyl)ethene (5i):
1H NMR (CDCl3, 300 MHz) δ 0.08 (s, 9H, Si(CH3)3), 0.33 (s, 9H,
Si(CH3)3), 7.39 (d, J ) 9.0 Hz, 2H, ArH), 7.46 (d, J ) 9.0 Hz, 2H,
ArH).
Representative Procedure for the Enantioselective Protonation
of Silyl Enol Ethers 3 with Stoichiometric Amounts of (R)-1‚SnCl4.
A heat-gun-dried 25 mL Schlenk flask containing (R)-1 (0.094 g, 0.33
mmol) was charged with dry toluene (6.6 mL, distilled from CaH2). A
solution of tin tetrachloride (0.3 mL, 0.3 mmol, 1.0 M) in dichlo-
romethane (or hexane) was added dropwise at room temperature. After
being stirred for 5 min at that temperature, the mixture was cooled to
-78 °C. Then starting material 3 (0.3 mmol) was added dropwise. After
being stirred for several hours at -78 °C, the mixture was poured into
saturated ammonium chloride, extracted with ether twice, dried over
MgSO4, filtered, and concentrated in vacuo. Purification of the crude
product by silica gel chromatography (eluent, 10:1 to 5:1 hexanes-
ethyl acetate) gave the pure product 4 as a white solid. The enantiomeric
excess of ketones was determined by HPLC analysis.
Representative Procedure for the Enantioselective Protonation
of Silyl Enol Ethers 3 with Catalytic Amounts of (R)-2‚SnCl4. Under
an argon atmosphere, to a solution of 7 (0.041 g, 0.33 mmol) in toluene
(5 mL) were added a solution of (R)-BINOL-Me 2 (1 mL, 0.006 mmol,
6 mM) in toluene and a solution of tin tetrachloride (0.15 mL, 0.15
mmol, 1 M) in dichloromethane. The mixture was stirred at ambient
temperature for 0.5 h. The solution was then cooled to -80 °C, and a
solution of 3 (0.3 mmol) in toluene (0.9 mL) was added dropwise along
the wall of the flask over a period of 2 h. After being stirred for a
further 5 min, the mixture was poured into saturated ammonium
chloride, extracted with ether twice, dried over MgSO4, filtered, and
concentrated in vacuo. Purification of the crude product by silica gel
chromatography (eluent, 10:1 to 5:1 hexanes-ethyl acetate) gave the
pure corresponding ketone 4 as a white solid. The enantiomeric excess
was determined by HPLC analysis.
1
1655 (CdC), 1254, 1211, 1138, 994, 849, 758, 698 cm-1; H NMR
(CDCl3, 300 MHz) δ -0.09 (s, 9H, Si(CH3)3), 0.29 (s, 9H, Si(CH3)3),
0.92 (t, J ) 7.5 Hz, 3H, CH3CH2), 2.37 (q, J ) 7.5 Hz, 2H, CH3CH2),
7.08-7.33 (m, 5H, C6H5); 13C NMR (CDCl3, 75 MHz) δ -0.03, 0.37,
13.50, 23.62, 101.49, 124.89, 127.54, 129.40, 140.40, 146.79; LR
FAB+-MS m/z 308 ([M]+, C16H28O2Si2 requires 308.6).
1,1-Bis(trimethylsilyloxy)-2-(4-isobutylphenyl)propene (5c): IR
(film) 2957, 1654 (CdC), 1254, 1213, 1140, 1067, 961, 849, 756 cm-1
;
1H NMR (CDCl3, 300 MHz) δ -0.05 (s, 9H, Si(CH3)3), 0.28 (s, 9H,
Si(CH3)3), 0.90 (d, J ) 6.6 Hz, 6H, (CH3)2CH), 1.85 (m, 1H,
(CH3)2CH), 1.90 (s, 3H, CH3CdC), 2.43 (d, J ) 7.1 Hz, 2H, (CH3)2-
CHCH2), 7.02 (d, J ) 8.2 Hz, 2H, ArH), 7.28 (d, J ) 8.2 Hz, 2H,
ArH); 13C NMR (CDCl3, 75 MHz) δ 0.05, 0.41, 16.55, 22.35, 30.32,
45.15, 94.40, 128.27, 128.30, 138.03, 138.85, 147.01; LR FAB+-MS
m/z 350 ([M]+, C19H34O2Si2 requires 350.7).
1,1-Bis(trimethylsilyloxy)-2-(6′-methoxy-2′-naphthyl)propene (5d):
1
IR (CCl4) 1655, 1605, 1480, 1254, 1200, 1134, 916, 853 cm-1; H
NMR (CDCl3, 300 MHz) δ -0.04 (s, 9H, Si(CH3)3), 0.02 (s, 9H, Si-
(CH3)3), 1.99 (s, 3H, CH3CdC), 3.91 (s, 3H, OCH3), 7.00-7.10 (m,
2H, ArH), 7.58-7.71 (m, 4H, ArH); 13C NMR (CDCl3, 75 MHz) δ
0.07, 0.41, 16.53, 55.08, 94.36, 105.43, 118.24, 125.54, 126.15, 128.23,
128.93, 129.04, 132.27, 136.88, 147.45, 156.96; LR FAB+-MS m/z
374 ([M]+, C20H30O3Si2 requires 374.6).
1,1-Bis(triethylsilyloxy)-2-methoxy-2-phenylethene (5e): IR (film)
2957, 1650 (CdC), 1597, 1458, 1414, 1262, 1138, 1026, 799, 764 cm-1
;
1H NMR (CDCl3, 300 MHz) δ 0.69 (q, J ) 7.9 Hz, 6H, Si(CH2CH3)3),
0.82 (q, J ) 7.8 Hz, 6H, Si(CH2CH3)3), 0.95 (t, J ) 7.9 Hz, 9H, Si-
(CH2CH3)3), 1.03 (t, J ) 7.8 Hz, 9H, Si(CH2CH3)3), 3.48 (s, 3H, OCH3),
7.07-7.58 (m, 5H, ArH); 13C NMR (CDCl3, 75 MHz) δ 5.08, 5.12,
6.54, 6.72, 58.62, 123.04, 124.71, 125.92, 127.73, 135.26, 146.10; LR
FAB+-MS m/z 394 ([M]+, C21H38O3Si2 requires 394.7).
Determination of Enantiomeric Excesses and Absolute Configu-
rations of 2-Arylcycloalkanones Produced by Enantioselective
Protonation of 2-Aryl-1-(trialkylsilyloxy)cyclohex-1-enes Using (R)-
1‚SnCl4 or (R)-2‚SnCl4 (Tables 1, 3, and 7). Enantiomeric ratios were
determined by analytical HPLC or chiral GC of the ketones. The
absolute configurations were determined by comparison of optical
rotation values with literature data.
Preparation of Ketene Bis(trimethylsilyl) Acetals 5f-i.12d To a
solution of LiHMDS (28 mmol) in THF (15 mL) was added a solution
of the carboxylic acid (10 mmol) in THF (50 mL) dropwise with stirring
at -78 °C, which was continued at -78 °C for a further 1 h. Excess
trimethylsilyl chloride (28 mmol) was added dropwise over 5 min, and
(S)-(-)-2-Phenylcyclohexanone (4a) (entry 1 in Table 1):2m,30a
HPLC (Daicel OD-H column, hexane:i-PrOH ) 200:1, flow rate 1 mL/
(30) (a) Berti, G.; Macchia, B.; Macchia, F.; Menti, L. J. Chem. Soc. C
1971, 3371. (b) Meyers, A. I.; Williams, D. R.; Erickson, G. W.; White,
S.; Druelinger, M. J. Am. Chem. Soc. 1981, 103, 3081.
(29) Gotthardt, H.; Weisshuhn, M. C.; Christl, B. Chem. Ber. 1976,
109, 9 (2), 740.