New Homochiral Pseudo-C2-symmetrical Ligands
J . Org. Chem., Vol. 64, No. 15, 1999 5587
(S)-4-Isop r op yl-1-tr im eth ylsiloxy-1-cycloh exen e (12c).
The reaction was carried out according to the typical procedure
using 4-isopropylcyclohexanone (70.0 mg, 0.50 mmol), urea 2
(320 mg, 0.63 mmol), n-BuLi (0.80 mL, 1.28 mmol, 1.6 M in
n-hexane), and TMSCl (0.32 mL, 2.52 mmol) to give silyl enol
ether 12c (90 mg, 84%; 87% ee) as a colorless oil: GC (CB,
100 kPa, 60 °C (1 min) to 140 °C, 2 °C/min): tR (min) ) 24.7
extracted with Et2O. The combined organic phases were
washed with brine and dried (Na2SO4). The solvent was
evaporated under reduced pressure, and the crude product was
purified by chromatography (pentane/Et2O 4:1 to 1:1), yielding
6c
benzyl tetralone 16
(180 mg, 83%; 81% ee) as colorless
crystals (mp 54 °C). The recovered urea 2 (350 mg, 69%) has
been reused for further reactions. HPLC (OD, 0.5% i-PrOH,
(S), 25.0 (R); [R]25 ) -187 (c ) 1.0, benzene) [lit.5c (R), 95%
0.6 mL/min, 254 nm): tR (min) ) 22.7 (R), 25.3 (S); [R]25
)
365
D
ee: [R]25 ) +217 (c ) 1.5, benzene)]; IR (film) 1671 cm-1
;
+15.1 (c ) 1.7, MeOH) [lit.6c (R), 92% ee: [R]25 ) +17.8 (c )
365
D
1H NMR (CDCl3, 200 MHz) δ 4.83 (m, 1H), 2.11-1.86 (m, 2H),
1.9, MeOH)]; 1H NMR (CDCl3, 300 MHz) δ 7.98 (m, 1H), 7.40-
7.32 (m, 1H), 7.27-7.09 (m, 7H), 3.40 (dd, J ) 3.6, 13.3 Hz,
1H), 2.89-2.78 (m, 2H), 2.71-2.50 (m, 2H), 2.18-1.96 (m, 1H),
1.78-1.61 (m, 1H); 13C NMR (CDCl3, 75 MHz) δ 199.3, 144.0,
140.0, 133.2, 132.5, 129.2, 128.7, 128.4, 127.5, 126.6, 126.1,
49.4, 35.7, 28.6, 27.7.
1.85-1.64 (m, 2H), 1.56-1.36 (m, 1H), 1.34-1.11 (m, 3H), 0.88
(d, J ) 6.8 Hz, 3H), 0.86 (d, J ) 6.6 Hz, 3H), 0.16 (s, 9H); 13
C
NMR (CDCl3, 50 MHz) δ 150.3, 103.8, 40.0, 32.0, 30.3, 27.3,
26.5, 20.1, 19.9, 0.3; MS (EI) m/z 212 (M+, 17%). Anal. Calcd
for C12H24OSi: C, 67.85; H, 11.39. Found: C, 67.71; H, 11.29.
(S)-4-P h en yl-1-tr im eth ylsiloxy-1-cycloh exen e (12d). The
reaction was carried out according to the typical procedure
using 4-phenylcyclohexanone (90.0 mg, 0.52 mmol), urea 2 (325
mg, 0.64 mmol), n-BuLi (0.80 mL, 1.28 mmol, 1.6 M in
n-hexane), and TMSCl (0.35 mL, 2.76 mmol) to give silyl enol
ether 12d (112 mg, 88%; 83% ee) as a colorless oil: GC (CB,
100 kPa, 70 °C (1 min) to 140 °C, 3 °C/min): tR (min) ) 32.8
(2R,4R)-3-Ch lor o-2,4-d ip h en ylp en ta n e (17). Carboxylic
acid 7 (8.10 g, 30.2 mmol) was converted to the corresponding
acid chloride by refluxing with thionyl chloride (18.0 g, 151
mmol) for 3 h. Excess reagent was evaporated in vacuo, and
the solid residue was dissolved in CCl4 (40 mL). This solution
was dropwise added (syringe pump) to a refluxing suspension
of the sodium salt of 2-mercaptopyridine-N-oxide (5.70 g, 36.3
mmol) and DMAP (380 mg, 3.11 mmol) in CCl4 (35 mL) under
argon while being irradiated with a photo lamp (300 W). After
the addition of the acid chloride, the lamp was switched off.
After refluxing for another 45 min, the brown reaction mixture
was cooled, diluted with pentane, and poured into 10% aqueous
HCl. The aqueous phase was extracted with pentane, and the
combined organic phases were washed with water and brine
and dried (MgSO4). After evaporation of the solvent under
reduced pressure, the crude product was purified by chroma-
tography (pentane/Et2O 40:1 to 10:1), yielding the alkyl
(S), 33.2 (R); [R]25 ) -120 (c ) 1.3, benzene) [lit.5c (R), 93%
365
ee: [R]25 ) +136 (c ) 1.5, benzene)]; IR (film) 1668 cm-1
;
365
1H NMR (CDCl3, 300 MHz) δ 7.25-7.06 (m, 5H), 4.86 (m, 1H),
2.74-2.58 (m, 1H), 2.27-2.04 (m, 3H), 2.03-1.69 (m, 3H), 0.13
(s, 9H); 13C NMR (CDCl3, 75 MHz) δ 150.3, 146.7, 128.4, 126.9,
126.0, 103.6, 40.0, 32.0, 30.2, 0.4; MS (EI) m/z 246 (M+, 44%).
Anal. Calcd for C15H22OSi: C, 73.11; H, 9.00. Found: C, 73.02;
H, 9.27.
(S)-4-ter t-Bu tyld im eth ylsiloxy-1-tr im eth ylsiloxy-1-cy-
cloh exen e (12e). The reaction was carried out according to
the typical procedure using 4-tert-butyldimethylsiloxycyclo-
hexanone (90.0 mg, 0.39 mmol), urea 2 (245 mg, 0.49 mmol),
n-BuLi (0.60 mL, 0.96 mmol, 1.6 M in n-hexane), and TMSCl
(0.25 mL, 1.97 mmol) to give silyl enol ether 12e (101 mg, 85%;
chloride 17 (6.60 g, 84%) as a colorless, waxy solid: mp 46-
1
48 °C; [R]25 ) +17.3 (c ) 1.9, CHCl3); H NMR (CDCl3, 300
D
MHz) δ 7.28-7.04 (m, 10H), 4.20 (dd, J ) 5.7, 7.5 Hz, 1H),
2.99-2.85 (m, 2H), 1.31 (d, J ) 7.1 Hz, 3H), 1.29 (d, J ) 6.9
Hz, 3H); 13C NMR (CDCl3, 75 MHz) δ 144.4, 142.4, 128.7,
128.5, 127.9, 127.7, 126.7, 126.6, 74.2, 43.5, 43.4, 20.7, 18.5;
MS (EI) m/z 258 (M+, 7%). Anal. Calcd for C17H19Cl: C, 78.90;
H, 7.40. Found: C, 79.00; H, 7.50.
88% ee) as a colorless oil: [R]25 ) -31.7 (c ) 0.4, CHCl3).
D
The enantiomeric excess was determined by comparison of the
optical rotation with literature data:18b (S), 80% ee: [R]25
)
D
-28.8 (c ) 0.3, CHCl3); 1H NMR (CDCl3, 300 MHz) δ 4.64 (m,
1H), 3.88-3.75 (m, 1H), 2.22-1.88 (m, 4H), 1.76-1.55 (m, 2H),
0.83 (s, 9H), 0.12 (s, 9H), 0.00 (m, 6H); 13C NMR (CDCl3, 75
MHz) δ 149.7, 101.3, 67.3, 33.3, 31.7, 28.1, 25.9, 18.1, 0.3, -4.6,
-4.7.
Bis{(2R)-p h en yl-1-[(R)-p h en ylet h yl]p r op yl}m et h yl-
p h osp h in e-Bor a n e Com p lex (3‚BH3). At -78 °C, a solution
of the alkyl chloride 17 (2.00 g, 7.73 mmol) in THF (4 mL)
was added to a vigorously stirred solution of lithium 4,4′-di-
tert-butylbiphenylide, prepared from 4,4′-di-tert-butylbiphenyl
(4.60 g, 17.3 mmol) and lithium pieces (107 mg, 15.4 mmol) in
THF (35 mL). Within 4 min, the blue color changed to dark
red. A solution of methyldichlorophosphine (320 mg, 2.74
mmol) in THF (1 mL) was added at -78 °C, instantaneously
causing discoloration. The cooling bath was removed, and the
reaction mixture was stirred at room temperature for 3 h
before BH3‚SMe2 (1.00 g, 13.2 mmol) was added. After the
mixture stirred at room temperature overnight, water (7 mL)
was carefully added, followed by Et2O (250 mL). The organic
layer was separated, and the aqueous phase was extracted
with Et2O. The combined organic phases were washed with
10% aqueous HCl and brine and dried (MgSO4). The solvents
were evaporated under reduced pressure, and the crude
product was purified by chromatography (aluminum oxide,
neutral, III; pentane/CH2Cl2 6:1, then pentane/Et2O/CH2Cl2
10:1:2 to 1:1:1), followed by crystallization from EtOAc yielding
phosphine-borane complex 3‚BH3 (1.12 g, 80%) as colorless
(1S,5R)-7,7-E t h ylen ed ioxy-3-t r im et h ylsiloxyb icyclo-
[3.3.0]oct-2-en (14). The reaction was carried out according
to the typical procedure using 7,7-ethylenedioxybicyclo[3.3.0]-
octan-3-one (13, 90.0 mg, 0.49 mmol), urea 2 (310 mg, 0.61
mmol), n-BuLi (0.76 mL, 1.22 mmol, 1.6 M in n-hexane), and
TMSCl (0.30 mL, 2.36 mmol) to give silyl enol ether 14 (114
mg, 91%; 86% ee) as a colorless oil: GC (CB, 100 kPa, 80 °C
(1 min) to 180 °C, 2 °C/min): tR (min) ) 25.1 (1S,5R), 25.4
(1R,5S); [R]25365 ) -31.4 (c ) 1.3, benzene) [lit.5g (1S,5R), 99%
ee: [R]25 ) -36.9 (c ) 3.1, benzene)]; IR (film) 1644 cm-1
;
365
1H NMR (CDCl3, 300 MHz) δ 4.54 (m, 1H), 3.82 (m, 4H), 3.22-
2.98 (m, 1H), 2.69-2.43 (m, 2H), 2.02-1.87 (m, 3H), 1.62-
1.47 (m, 2H), 0.13 (s, 9H); 13C NMR (CDCl3, 75 MHz) δ 153.0,
117.9, 107.3, 64.6, 63.9, 43.2, 42.6, 41.4, 40.4, 35.8, 0.0; MS
(EI) m/z 254 (M+, 13%). Anal. Calcd for C13H22O3Si: C, 61.38;
H, 8.72. Found: C, 61.20; H, 8.40.
Typ ica l P r oced u r e for th e En a n tioselective Alk yla -
tion . (R)-2-Ben zyl-3,4-d ih yd r o-2H-n a p h th a len -1-on e (16).
At -78 °C, n-BuLi (0.67 mL, 1.00 mmol, 1.5 M in n-hexane)
was dropwise added to a solution of urea 2 (505 mg, 1.00 mmol)
in THF (7 mL). The solution was allowed to warm to 0 °C over
15 min and stirred for a further 15 min. After the mixture
cooled to -40 °C, a solution of 1-tetralone (120 µL, 0.90 mmol)
in THF (2 mL) was slowly added. The cooling bath was
removed, and the homogeneous solution was stirred at room
temperature for 40 min. After the mixture cooled back to -78
°C, a solution of benzyl bromide (1.20 mL, 10.1 mmol) in THF
(2 mL) was dropwise added in 15 min. The reaction mixture
was allowed to warm to -20 °C and stirred for a further 24 h
before the addition of 1 M HCl (5 mL) and Et2O (80 mL). The
organic layer was separated, and the aqueous phase was
crystals: mp 136-138 °C; [R]25 ) -161.8 (c ) 1.1, CHCl3);
D
IR (KBr) 2370 cm-1; H NMR (CDCl3, 500 MHz) δ 7.10-6.80
1
(m, 16H), 6.72-6.67 (m, 4H), 4.17-4.10 (m, 1H), 3.60-3.51
(m, 1H), 3.42-3.35 (m, 1H), 3.33-3.25 (m, 1H), 3.13-3.07 (m,
1H), 2.98-2.94 (m, 1H), 1.82 (d, J ) 8.6 Hz, 3H), 1.61 (d, J )
7.3 Hz, 3H), 1.56 (d, J ) 6.9 Hz, 3H), 1.49 (d, J ) 7.2 Hz, 6H),
1.75-0.65 (br, 3H); 13C NMR (CDCl3, 125 MHz) δ 146.0 (d, J
) 13.8 Hz), 145.1 (d, J ) 10.1 Hz), 144.8 (d, J ) 11.3 Hz),
144.3 (d, J ) 7.6 Hz), 127.9-127.6 (m), 127.4, 126.8 (m), 126.0,
125.7, 125.1, 124.9, 47.7 (d, J ) 20.1 Hz), 47.2 (d, J ) 21.4
Hz), 38.2-37.9 (m), 24.3-24.1 (m), 14.1 (m), 10.4 (d, J ) 31.4
Hz); 31P NMR (CDCl3, 81 MHz) δ 34.5 (br); MS (FD) m/z 506