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T. Hashimoto et al. / Tetrahedron 63 (2007) 12883–12887
commercially available. Other cinnamates and the unsatu-
rated esters were prepared from the corresponding acid chlo-
ride or acids with alcohols.
4.2.2. The coupling of a-naphthoaldehyde (28) and iso-
propyl cinnamate (15) and subsequent dehydroxylation
(Scheme 6). The rhodium complex 3 [Rh(Phebox-ip)-
(OAc)2(H2O)] (2.7 mg, 0.005 mmol), isopropyl cinnamate
(15) (143 mg, 0.75 mmol), and p-anisaldehyde (78 mg,
0.5 mmol) were placed in a 10 mL-flask. Under an argon at-
mosphere, toluene (0.5 mL) was added at room temperature,
and then methyldiphenylsilane (159 mg, 0.8 mmol) was
slowly added at 50 ꢀC by syringe. The mixture was stirred
for 0.5 h. The reaction was monitored by TLC examination.
EtOH (1.0 ml) was added and the mixture was concentrated.
Then, THF (1.0 mL), MeOH (1 mL), TBAF (0.5 mL, 1 M in
THF), and KF (290 mg, 5.0 mmol) were added at 0 ꢀC, and
the mixture was stirred at 50 ꢀC for 48 h. TLC, Rf¼0.45 for
aldol product (eluent: EtOAc/hexane¼1:3). The mixture
was extracted with EtOAc (5 mLꢁ3). The combined organic
layer was washed with saturated brine (5 mL), and then dried
over MgSO4. After concentration, the residue was purified by
silica gel column chromatography with EtOAc/hexane as el-
uent to give the crude aldol mixture (169 mg, 0.48 mmol);
4.2. Typical reactions
4.2.1. The coupling of p-anisaldehyde (6) and isopropyl
cinnamate (15) and subsequent reductive dehydroxy-
lation (entry 1, Table 1). The rhodium complex 3 [Rh(Phe-
box-ip)(OAc)2(H2O)] (5.4 mg, 0.01 mmol), isopropyl
cinnamate (15) (285 mg, 1.5 mmol), and p-anisaldehyde
(136 mg, 1.0 mmol) were placed in a 10 mL-flask. Under an
argon atmosphere, toluene (1.0 mL) was added at room tem-
perature, and then methyldiphenylsilane (317 mg, 1.6 mmol)
was slowlyadded at50 ꢀC bysyringe. Themixturewas stirred
for 0.5 h. The reaction was monitored by TLC examination.
After concentration, THF (1.0 mL), MeOH (1 mL), aq HCl
(1 mL, 4 N), and KF (232 mg, 4.0 mmol) were added at
0 ꢀC, and the mixture was stirred at room temperature for
24 h. TLC, Rf¼0.33 for syn-aldol product and Rf¼0.24 for
anti-aldol product (eluent: EtOAc/hexane¼1:3). The mixture
was treated with aq NaHCO3 (ca. 15 mL), and was extracted
with EtOAc (5 mLꢁ3). The combined organic layer was
washed with saturated brine (5 mL), and then dried over
MgSO4. Afterconcentration, the residuewaspurifiedbysilica
gel column chromatography with EtOAc/hexane as eluent to
give the aldol product in 93% yield (307 mg, 0.93 mmol) as
colorless oil; anti/syn¼90:10, by 1H NMR. Colorless oil. 1H
NMR (300 MHz, CDCl3) anti: d 0.93 (d, J¼6.3 Hz, 3H),
1.04 (d, J¼6.0 Hz, 3H), 2.74 (dd, J¼13.2, 5.4 Hz, 1H), 2.85–
3.05 (m, 2H), 3.81 (s, 3H), 4.78 (d, J¼6.6 Hz, 1H), 4.88 (m,
1H), 6.88 (d, J¼8.7 Hz, 2H), 7.11–7.30 (m, 7H); for syn:
1
anti/syn¼>99:<1 by H NMR. To a solution of the aldol
mixture (169 mg) in trifluoroacetic acid (0.36 mL) was
added triethylsilane (0.15 mL, 0.96 mmol) at 0 ꢀC. The mix-
turewas stirred for 3 h at room temperature. The reaction was
monitored by TLC examination; Rf¼0.75 (eluent: EtOA/
hexane¼1:3). The mixture was treated with aq NaHCO3
(ca. 12 mL), and was extracted with EtOAc (5 mLꢁ3). The
combined organic layer was washed with saturated brine
(5 mL), and then dried over MgSO4. After concentration,
the residuewas purified by silica gel column chromatography
with EtOAc/hexane as eluent to givethe desired product 29 in
1
87% yield (145 mg, 0.44 mmol) as colorless oil. H NMR
d 0.83 (d, J¼6.3). IR (neat) n 3475, 1715 (C]O) cmꢂ1
.
(300 MHz, CDCl3) d 0.89 (d, J¼6.3 Hz, 3H), 0.95 (d,
J¼6.3 Hz, 3H), 2.87 (m, 1H), 3.04–3.15 (m, 2H), 3.28 (m,
1H), 3.39 (m, 1H), 4.81 (sept, J¼6.3 Hz, 1H), 7.17–7.38
(m, 6H), 7.43–7.49 (m, 2H), 7.71 (m, 1H), 7.78–7.86 (m,
2H). 13C NMR (75 MHz, CDCl3) d 21.6, 21.7, 35.4, 38.8,
49.0, 67.5, 123.3, 125.1, 125.2, 125.7, 126.2, 126.9, 127.0,
128.1, 128.5, 128.8, 131.6, 133.6, 135.0, 138.8, 174.2. IR
(neat) n 1725 (C]O) cmꢂ1. EI-HRMS: [M+] m/z, found:
332.1772; calcd (C23H24O2): 332.1776. Chromatography:
DAICEL CHIRALCEL OD-H, eluent: hexane/2-propanol
(90:10) (0.7 mL/min), retention time; 7.5 min (minor),
8.2 min (major), 96% ee; [a]2D3 ꢂ21.8 (c 2.1, CHCl3).
EI-HRMS: [M+] m/z, found: 328.1678; calcd (C20H24O4):
328.1675. Chromatography: DAICEL CHIRALPAK AS-H,
eluent: hexane/2-propanol (90:10) (1.0 mL/min), retention
time; 5.8 min (syn, major), 6.5 min (syn, minor), 7.2 min
(anti, minor), 9.5 min (anti, major), syn 81% ee, anti 95% ee.
To a solution of the aldol mixture (256 mg, 0.78 mmol) in
trifluoroacetic acid (0.58 mL) was added triethylsilane
(0.27 mL, 1.7 mmol) at 0 ꢀC. The mixture was stirred for
0.5 h at room temperature. The reaction was monitored by
TLC examination; Rf¼0.68 (eluent: EtOAc/hexane¼1:3).
The mixture was treated with aq NaHCO3 (ca. 15 mL),
and was extracted with EtOAc (5 mLꢁ3). The combined
organic layer was washed with saturated brine (5 mL), and
then dried over MgSO4. After concentration, the residue
was purified by silica gel column chromatography with
EtOAc/hexane as eluent to give the desired product 21 in
97 % yield (236 mg, 0.76 mmol) as colorless oil (92% for
2 steps). 1H NMR (300 MHz, CDCl3) d 0.97 (d, J¼6.2 Hz,
3H), 0.99 (d, J¼6.2 Hz, 3H), 2.72–2.97 (m, 5H), 3.78 (s,
3H), 4.83 (sept, J¼6.2 Hz, 1H), 6.79 (d, J¼8.5 Hz, 2H),
7.08 (d, J¼8.5 Hz, 2H), 7.16–7.27 (m, 5H). 13C NMR
(75 MHz, CDCl3) d 21.7, 21.8, 37.7, 38.4, 50.0, 55.3,
67.4, 113.5, 126.1, 128.1, 128.7, 129.7, 131.0, 139.0,
157.8, 174.1. IR (neat) n 1726 (C]O) cmꢂ1. EI-HRMS:
[M+] m/z, found: 312.1721; calcd (C20H24O3): 312.1725.
Chromatography: DAICEL CHIRALCEL OJ-H, eluent:
hexane/2-propanol (90:10) (0.7 mL/min), retention time;
11.1 min (major), 12.3 min (minor), 93% ee; [a]2D5 +3.2
(c 2.1, CHCl3).
4.3. X-ray diffraction study
Single crystals of 31 suitable for X-ray diffraction study were
obtained from hexane/ethyl acetate solution at 0 ꢀC. The dif-
fraction data were collected on a Brucker SMART APEX
CCD diffractometer with graphite monochromated Mo Ka
˚
radiation (l¼0.71073 A). An empirical absorption correc-
tionwas applied byusingSADABS. The structurewas solved
by direct method and refined by full-matrix least-square
on F2 using SHELXTL. All non-hydrogen atoms were re-
fined with anisotropic displacement parameters. All hydro-
gen atoms were located on calculated positions and refined
as rigid groups. Refinement details: empirical formula;
C27H33NO4S; Mr¼467.60; temperature 173(2) K; crystal
system: triclinic; space group: P212121; a¼10.617(4),
3
˚
˚
b¼12.996(4), c¼17.630(6) A, V¼2432.4(14) A , Z¼4,
rcalcd¼1.277 Mg/m3, m¼0.167 mmꢂ1, F(000)¼1000, crys-
tal size¼0.50ꢁ0.20ꢁ0.10 mm3, q range¼1.95 to 27.53ꢀ;