Vol. 64, No. 7 (2016)
Chem. Pharm. Bull.
933
tadienides 1 promote the hydrolysis of TBS ether 3 in a (0.0055mmol, 0.05 equiv) in 1M HCl (0.3mL) was added, fol-
CH2Cl2–1 M HCl biphasic solvent system via the formation of lowed by vigorous manual shaking. The mixture was allowed
lipophilic hydronium salt 2. The capability of 2 as a phase- to stand for the indicated time. The yields were calculated
1
transfer catalyst was also demonstrated by experiments con- on the basis of the integration of the H-NMR signals of L-
ducted using a triphasic system with a right-angled U-tube. menthol (0.74ppm for methyl group) and benzene (7.37ppm).
Currently, more experiments for verifying the synthetic utility
of catalyst 1 is underway in our laboratory.
General Procedure of the U-Tube Experiment for the
C5Ph(CN)4 Salt Solubility in CH2Cl2 (Table 2) A right-
angled U-tube equipped with two glass sticks and three
magnetic stir bars (Fig. 4) was charged with a solution of
Experimental
Hydrolysis of TBS Ether 3 in a Biphasic System Using an additive (0.75mmol) in CH2Cl2 (20mL). A solution of 1c
Catalyst 1a (Table 1, Entry 4) To a solution of TBS ether (8mg, 0.03mmol) in 1M HCl or H2O (3mL) was added to one
328) (100mg, 0.37mmol) in CH2Cl2 (1.0mL) was added 1M side of the U-tube (phase A), and 1M HCl or H2O (3mL) was
HCl (0.50mL, 0.50mmol) and tetracyanocyclopentadienide added to the other side (phase B), and the system was stirred
1a (7.4mg, 0.02mmol) and the reaction mixture was stirred at a rate of approx. 1000rpm. The amount of the C5Ph(CN)4
for 2h. The reaction was quenched with saturated aq NaHCO3 anion was measured at the indicated time according to the
and the mixture was extracted with EtOAc. The extract was following procedures. A 10µL sample was collected using a
washed with brine, dried over Na2SO4, filtered, and concen- micropipette and diluted with a 0.025% (w/v) phenol aqueous
trated under reduced pressure. Purification by flash chroma- solution in a 5mL volumetric flask. The resulting solution was
tography (20% EtOAc in n-hexane) afforded L-menthol (53mg, analyzed by HPLC (Develosil C30-UG-5, 70% MeOH/25mM
92%). Further elution with EtOAc provided recovered 1a aqueous Na2HPO4, 0.8mL/min, 254nm, 5.7min for phenol
(6.4mg, 86% recovered).
and 9.5min for 1c), and the percentages of the remaining
L-Menthol. 1H-NMR (CDCl3, 500MHz) δ: 3.40 (1H, td, C5Ph(CN)4 anion in phase A or the transferred C5Ph(CN)4
J=10.4, 4.4Hz), 2.18 (1H, sptd, J=7.0, 2.7Hz), 1.96 (1H, dtd, anion to phase B were calculated on the basis of the initial
J=12.1, 3.9, 2.1Hz), 1.66 (1H, dqd, J=3.2, 2.5Hz), 1.61 (1H, amount of 1c in phase A.
dq, J=12.9, 3.2Hz), 1.56 (1H, brs), 1.42 (1H, tqt, J=11.5, 7.0,
3.4Hz), 1.11 (1H, ddt, J=12.4, 9.8, 3.1Hz), 1.01–0.81 (3H, m),
0.93 (3H, d, J=7.0Hz), 0.91 (3H, d, J=7.0Hz), 0.81 (3H, d, a Grant-in-Aid for Scientific Research (C) (24590033), Grant-
J=7.0 Hz).29)
in-Aid for Young Scientists (B) (26860018) from the Japan
Acknowledgments This study was partially supported by
Hydrolysis of Acetonide 5 in a Biphasic System Using Society for the Promotion of Science (JSPS), and the Science
Catalyst 1c (Eq. 1) To a solution of acetonide 530) (100mg, Research Promotion Fund from the Promotion and Mutual Aid
0.56mmol) in CH2Cl2 (1.5mL) was added 1M HCl (0.75mL) Corporation for Private Schools of Japan.
and catalyst 1c (7.4mg, 0.028mmol), and the reaction mixture
was stirred for 2h. The reaction was quenched with saturated
Conflict of Interest The authors declare no conflict of
aq NaHCO3 and the mixture was extracted with EtOAc. The interest.
extract was washed with brine, dried over Na2SO4, filtered,
and concentrated under reduced pressure. Purification by flash
Supplementary Materials The online version of this ar-
chromatography (80% EtOAc in n-hexane) afforded diol 6 ticle contains supplementary materials.
(53mg, 92%). Further elution with EtOAc provided recovered
1c (6.0mg, 81% recovered).
Diol 6. H-NMR (CDCl3, 500MHz) δ: 7.36–7.26 (5H, m),
References and Notes
1
1) “Phase-Transfer Catalysis Mechanisms and Syntheses,” ed. by
Halpern M. E., ACS Symposium Series 659, American Chemical
4.81 (1H, dd, J=8.1, 3.4Hz), 3.74 (1H, dd, J=11.3, 3.4Hz), 3.66
(1H, dd, J=11.3, 8.1Hz), 2.88 (1H, brs), 2.44 (1H, brs).29)
Acid-Catalyzed Rearrangement of cis-Stilbene Oxide (7)
to Aldehyde 8 (Eq. 2) To a solution of cis-stilbene oxide
(7) (50.0mg, 0.25mmol) in CH2Cl2 (1mL) was added 1M HCl
(0.5mL) and catalyst 1e (2.9mg, 0.014mmol), and the reac-
tion mixture was stirred for 24h. The reaction was quenched
with saturated aq NaHCO3 and the mixture was extracted
with EtOAc. The extract was washed with brine, dried over
Na2SO4, filtered, and concentrated under reduced pressure.
Purification by flash chromatography (10% Et2O in n-hexane)
afforded diol 6 (28.2mg, 58%). Further elution with EtOAc
provided recovered 1e (1.9mg, 66% recovered).
3) “Asymmetric Phase Transfer Catalysis,” ed. by Maruoka K., Wiley-
1
Aldehyde 8. H-NMR (CDCl3, 500MHz) δ: 9.94 (1H, d,
J=2.5Hz), 7.40–7.34 (4H, m), 7.30 (2H, tt, J=7.3, 1.5Hz),
7.24–7.20 (4H, m), 4.89 (1H, d, J=2.5 Hz).29)
General Procedure for the NMR Experiment of the
Hydrolysis of TBS Ether 3 in a Biphasic System (Fig. 3)
An NMR tube was charged with a solution of TBS ether 3
(30mg, 0.11mmol) and benzene (internal standard, 10µL) in
CD2Cl2 (0.6mL). A solution of tetracyanocyclopentadienide 1