Methyltrioxorhenium-catalyzed epoxidation of homoallylic alcohols with hydrogen peroxide

Article abstract of DOI:10.1021/jo301825j

Homoallylic alcohols were efficiently converted to the corresponding 3,4-epoxy alcohols in excellent yields by methyltrioxorhenium (MTO)-catalyzed epoxidation with aqueous hydrogen peroxide as the terminal oxidant and 3-methylpyrazole (10 mol %) as an add

Full text of DOI:10.1021/jo301825j

Note
pubs.acs.org/joc
Methyltrioxorhenium-Catalyzed Epoxidation of Homoallylic Alcohols
with Hydrogen Peroxide
Shigekazu Yamazaki*
Toyama Industrial Technology Center, 150 Futagami, Takaoka, Toyama 933-0981, Japan
S
* Supporting Information
ABSTRACT: Homoallylic alcohols were efficiently converted to
the corresponding 3,4-epoxy alcohols in excellent yields by
methyltrioxorhenium (MTO)-catalyzed epoxidation with aqueous
hydrogen peroxide as the terminal oxidant and 3-methylpyrazole
(10 mol %) as an additive. The epoxidations of homoallylic
alcohols proceeded under organic solvent-free conditions faster
than those in dichloromethane.
poxidation of alkenes is an important transformation
because epoxides are valuable synthetic intermediates.1
for homoallylic alcohol epoxidation using hydrogen peroxide as
the terminal oxidant.16,17
Here we report the results of detailed examination of MTO-
catalyzed epoxidation of various homoallylic alcohols to the
corresponding 3,4-epoxy alcohols with hydrogen peroxide as
the terminal oxidant.
E
Development of catalytic epoxidation methods using an
environmentally benign oxidant such as hydrogen peroxide is
currently of interest because it produces water as the only waste
byproduct and has advantages of cost and atom efficiency.2,3
Methyltrioxorhenium (MTO, CH3ReO3) is one of the most
efficient and well-studied epoxidation catalyst using hydrogen
peroxide as the oxidant. Since the original finding of the
properties of MTO as an epoxidation catalyst in 1991,4 a large
number of studies related to MTO-catalyzed epoxidation have
been reported.5,6
At first, the epoxidation of trans- and cis-3-hexen-1-ol was
examined (Scheme 1 and Table 1). The epoxidation of trans-3-
Scheme 1. Epoxidation of trans- and cis-3-Hexen-1-ol
Epoxy alcohols are useful intermediates in organic synthesis.7
The syntheses of some epoxy alcohols by MTO-catalyzed
epoxidation of alkenols have been reported. MTO-catalyzed
epoxidation of allylic alcohols has been explored extensively
including the diastereoselectivity, kinetics, and reaction
mechanism.8 Moreover, MTO-catalyzed epoxidation of bisho-
moallylic alcohols has been explored, and the formation of
furan compounds by intramolecular cyclization of 4,5-epoxy
alcohols initially formed9 and an isolation method of acid-
sensitive 4,5-epoxy alcohols have also been reported.6c
On the other hand, only a few homoallylic alcohols (cis- and
trans-3-hexen-1-ol, 1-nonen-4-ol) were reported on MTO-
catalyzed epoxidation.10 The 3,4-epoxy alcohols, prepared by
epoxidation of homoallylic alcohols, are also known as useful
synthetic intermediates.7 Although vanadium,11 zirconium,12
molybdenum,13 titanium,14 and hafnium12c complexes have
been reported as the catalysts for epoxidation of homoallylic
alcohols, the epoxidations using these catalysts require alkyl
hydroperoxides (such as tert-butyl hydroperoxide and cumene
hydroperoxide) as the terminal oxidant. Tungstic acid has been
reported to catalyze the epoxidation of homoallylic alcohols
with hydrogen peroxide, but the yields of epoxides are only
moderate.15 Recently reported selenium-containing dinuclear
peroxotungstate has been known as the sole effective catalyst
hexen-1-ol 1a with 1.2 equiv of 35% hydrogen peroxide as an
oxidant, 0.2 mol % of MTO as the catalyst, and 10 mol % of 3-
methylpyrazole (3-MePz) as the additive6a−c in dichloro-
methane resulted in the formation of corresponding trans-
epoxide 2a in 95% yield by 8 h reaction at 20 °C (entry 1).
Dichloromethane is the most commonly used solvent for
MTO-catalyzed epoxidation because fast rate, high yield, and
high selectivity are obtained by using this solvent.5b In a similar
manner, the epoxidation of cis-3-hexen-1-ol 1b with 0.1 mol %
of MTO in dichloromethane afforded 98% yield of cis-epoxide
2b at 20 °C within a 5 h reaction (entry 3). The epoxidation
proceeded with retention of the stereochemistry around the
olefinic bonds of the substrates. The reaction times can be
Received: August 27, 2012
Published: October 5, 2012
© 2012 American Chemical Society
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Note
epoxidation of cyclohexene 1c, which does not have a hydroxyl
group, using dichloromethane as the solvent and without
organic solvent were comparable (entries 5 and 6).
Table 1. MTO-Catalyzed Epoxidation of trans-3-Hexen-1-ol,
cis-3-Hexen-1-ol, and Cyclohexene
a
MTO
temp
time
%
b
The concentration of hydrogen peroxide in organic phase
(substrate 3-hexen-1-ol) during the epoxidations of 1a and 1b
under organic solvent-free conditions must be higher than that
in dichloromethane because the substrate alkenols have a
hydroxyl group. The higher concentration of hydrogen
peroxide enhances the rate of the formation of the catalytically
active peroxo species.6b This must be the reason for faster rates
of epoxidation of 1a and 1b under organic solvent-free
conditions than for those in dichloromethane.
Similarly, the epoxidations of cis-3-hepten-1-ol 1d, cis-3-
octen-1-ol 1e, and cis-3-nonen-1-ol 1f were examined. These
homoallylic alcohols afforded over 90% yield of corresponding
3,4-epoxy alcohols 2d−f both in dichloromethane and without
organic solvent conditions (Table 2, entries 1−6). Again, faster
rates of epoxidation under organic solvent-free conditions than
in dichloromethane were observed. However, the differences of
the rates of epoxidations that use and do not use organic
solvent become small by increasing molecular size of the
substrates. This might be because increasing molecular size of
the homoallylic alcohols causes increasing hydrophobicity that
leads to lower concentration of hydrogen peroxide in organic
entry
1
substrate
solvent
(mol %)
(°C)
(h) epoxide
trans-3-hexen-1- CH2Cl2
ol (1a)
0.2
0.2
0.1
0.1
0.2
0.2
20
10
20
10
20
20
8
95
>99
98
2
3
4
5
6
trans-3-hexen-1-
ol (1a)
c
1.5
5
cis-3-hexen-1-ol
(1b)
CH2Cl2
cis-3-hexen-1-ol
(1b)
c
1
>99
>99
>99
cyclohexene
(1c)
CH2Cl2
2
cyclohexene
(1c)
c
2
a
Alkene (10 mmol), 35% H2O2 (12 mmol), 3-methylpyrazole (1
b
mmol), in CH2Cl2 (5 mL) or without organic solvent. Analysis by
GC. Reaction without organic solvent.
c
reduced drastically by performing the reactions under organic
solvent-free conditions even at lower temperature (10 °C).6b
The alkenols 1a and 1b were converted to the corresponding
3,4-epoxy alcohols 2a and 2b quantitatively within 1.5 and 1 h,
respectively (entries 2 and 4). On the other hand, the rates of
a
Table 2. MTO-Catalyzed Epoxidation of Homoallylic Alcohols
a
b
c
Alkenol (10 mmol), 35% H2O2 (12 mmol), 3-methylpyrazole (1 mmol), in CH2Cl2 (5 mL) or without organic solvent. Analysis by GC. Yields
d
e
f
based on alkenols used. Reaction without organic solvent. Isolated yield of 10 g scale reaction. See Experimental Section for detail. 3-
Methylpyrazole (1 mmol) and 1-methylimidazole (0.1 mmol) were used as additives. Isolated yield. H2O2 (15 mmol). Isolated yield of 15 mmol
g
h
i
scale reaction by Kugelrohr distillation. See Experimental Section for detail.
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Note
phase (homoallylic alcohols under organic solvent-free
conditions). The lower hydrogen peroxide concentration in
the organic phase resulted in a slower rate of epoxidation.
Epoxidation of 3-methyl-3-buten-1-ol 1g gave corresponding
3,4-epoxy alcohol 2g in high yield (entries 7 and 8). The
reaction times required for these epoxidations were 8 h at 20
°C in dichloromethane and 1.5 h at 10 °C under organic
solvent-free conditions. The difference of the rates of
epoxidation of this five-carbon substrate in dichloromethane
and without organic solvent is comparable to that of trans-3-
hexen-1-ol 1a, a six-carbon substrate. In the case of the
epoxidation of 1g without organic solvent, the phase of the
reaction mixture that was separated to an organic (1g) and
aqueous layer at the beginning of the reaction became
homogeneous gradually as the reaction proceeded.
Homoallylic alcohols that have disubstituted and trisubstituted
alkene moieties afforded over 90% yield of epoxides with 0.1−
0.2 mol % of MTO, and those with terminal alkene also
afforded high yield of epoxides with 0.5−1 mol % of MTO with
prolonged reaction time. We also found that in the case of small
homoallylic alcohols (that have 4−10 carbons), the rates of
epoxidations without organic solvent are faster than those in
dichloromethane. Unfortunately, the MTO-catalyzed oxidation
of acyclic secondary homoallylic alcohols afforded epoxides
without stereoselectivity.
EXPERIMENTAL SECTION
■
General. Methyltrioxorhenium was prepared according to the
reported procedure.18 1-Phenyl-3-buten-1-ol 1i and 6-methyl-1-
hepten-4-ol 1j were prepared according to the reported procedure.19
The concentration of H2O2 was determined by iodometric titration
before use. The progress of the reaction was monitored by GC analysis
(FID detector). The conversion of alkenols and yield of epoxides were
determined by GC internal standard technique. GC analyses were
performed using GL Sciences InertCap 1 column (30 m length × 0.25
mm i.d., 0.25 μm polydimethylsiloxane film thickness).
Epoxidation of ( )-terpinen-4-ol 1h produced a small
amount of triol 3 as byproduct which was a hydrolysis product
of the initially formed epoxide 2h under the reaction conditions
(Scheme 2). The ratio of triol 3 increased gradually on standing
Scheme 2. Epoxidation of ( )-Terpinen-4-ol 1h
General Procedure of Homoallylic Alcohol Epoxidation
(Table 1, entry 3). A 50 mL flask equipped with a stirbar was
charged with CH2Cl2 (5 mL), cis-3-hexen-1-ol 1b (1.18 mL, 10
mmol), 3-methylpyrazole (81 μL, 1.0 mmol, 10 mol %), and MTO
(2.5 mg, 0.010 mmol, 0.1 mol %). The mixture was maintained at 20
°C by immersing in a temperature-controlled water bath. H2O2 (35%,
1.01 mL, 12 mmol) was added all at once to the stirring solution. The
resulting two-phase mixture was stirred vigorously at 20 °C. The
progress of the reaction was monitored at appropriate intervals by GC
analysis of small aliquots of the organic phase. The conversion of 1b
and yield of epoxide 2b were determined by a GC internal standard
method. The GC internal standard material (n-undecane) was added
just before the first analysis. The epoxide was isolated and identified in
a separate experiment as follows. The reaction mixture was poured
into brine and extracted with CH2Cl2. The organic layer was washed
successively with brine and aqueous Na2S2O3. Then the organic layer
was washed with aqueous solution of tartaric acid to remove 3-
methylpyrazole, followed with aqueous solution of NaHCO3. The
organic layer was dried over anhydrous Na2SO4, and CH2Cl2 was
distilled out by an evaporator. The oily residue obtained was dried
under vacuum. The crude epoxide was purified by Kugelrohr
distillation under reduced pressure.
the reaction mixture at ambient temperature. When the
epoxidation of 1h was performed with the addition of 1 mol
% of 1-methylimidazole (1-MeIm) that strongly inhibits the
hydrolysis of epoxides,6c 96% yield of epoxide was obtained by
1 h reaction at 10 °C in dichloromethane (entry 9). No
hydrolysis product 3 was detected under the conditions. The
cis/trans ratio of 2h was 88/12, which was higher than that of
CH3CO3H/NaOAc epoxidation (cis/trans ratio, 79:21) and
was lower than those of the epoxidations using H2O2/NaWO4
(93:7), TBHP/VO(acac)2 (>90:1), and H2O2/CH3CN/K2CO3
(>90:1).17 The epoxidation of 1h under similar conditions
without organic solvent resulted in creamy form within 1 h, and
the progress of the reaction stopped.
The rate of the epoxidation of 1-phenyl-3-buten-1-ol 1i, a
terminal alkene, was slower than those of disubstituted and
trisubstituted alkenols examined above (1a−h). The conversion
at 8 h with a larger amount of MTO (0.5 mol %) is 79% in
dichloromethane and 90% without organic solvent (entries 10
and 11). Similarly, a larger amount of MTO was required for
good conversion of other terminal alkenes, 6-methyl-1-hepten-
4-ol 1j and 3-buten-1-ol 1k (entries 12−15). No stereo-
selectivity was observed for MTO-catalyzed epoxidation of 1i
and 1j (both of cis/trans ratios of 2i and 2j were 50/50),10b
while some homoallylic alcohol epoxidation systems show cis-
selectivity (e.g., VO(acac)2/TBHP11d and H2O2/CH3CN/
K2CO3;17 epoxidation of 1i and 1j with H2O2/CH3CN/
K2CO3 afforded epoxides with cis/trans ratio of 64/36 and 68/
32, respectively).
trans-3,4-Epoxy-1-hexanol (2a).11b,12b,c,16 1H NMR (400 MHz,
CDCl3): δ 1.00 (t, J = 7.6 Hz, 3H), 1.50−1.65 (m, 2H), 1.65−1.76 (m,
1H), 1.92−2.02 (m, 1H), 2.29 (br, 1H), 2.76−2.81 (m, 1H), 2.86−
2.91 (m, 1H), 3.75−3.82 (m, 2H). 13C NMR (100 MHz, CDCl3): δ
9.8, 24.9, 34.2, 56.6, 59.4, 59.9.
cis-3,4-Epoxy-1-hexanol (2b).11b,12b,16 1H NMR (400 MHz,
CDCl3): δ 1.05 (t, J = 7.6 Hz, 3H), 1.47−1.74 (m, 3H), 1.83−1.92 (m,
1H), 2.92 (br, 1H), 2.90−2.96 (m, 1H), 3.08−3.14 (m, 1H), 3.77−
3.89 (m, 2H). 13C NMR (100 MHz, CDCl3): δ 10.3, 21.1, 30.4, 55.0,
57.9, 60.2.
cis-3,4-Epoxy-1-heptanol (2d).11b 1H NMR (400 MHz,
CDCl3): δ 0.95−1.02 (m, 3H), 1.43−1.59 (m, 4H), 1.64−1.74 (m,
1H), 1.84−1.93 (m, 1H), 2.38 (br, 1H, OH), 2.94−2.99 (m, 1H),
3.07−3.13 (m, 1H), 3.79−3.91 (m, 2H). 13C NMR (100 MHz,
CDCl3): δ 13.9, 19.7, 29.8, 30.5, 54.9, 56.6, 60.5.
cis-3,4-Epoxy-1-octanol (2e).11b,12c,16 1H NMR (400 MHz,
CDCl3): δ 0.93 (t, J = 7.1 Hz, 3H), 1.33−1.60 (m, 6H), 1.61−1.75 (m,
1H), 1.84−1.93 (m, 1H), 2.21 (m, 1H, OH), 2.92−2.99 (m, 1H),
3.07−3.13 (m, 1H), 3.75−3.92 (m, 2H). 13C NMR (100 MHz,
CDCl3): δ 13.9, 22.5, 27.6, 28.5, 30.5, 55.0, 56.8, 60.6.
cis-3,4-Epoxy-1-nonanol (2f).11b,16 1H NMR (400 MHz,
CDCl3): δ 0.90 (t, J = 7.1 Hz, 3H), 1.27−1.60 (m, 8H), 1.64−1.76
(m, 1H), 1.82−1.94 (m, 1H), 2.05 (br, 1H, OH), 2.92−3.00 (m, 1H),
3.07−3.14 (m, 1H), 3.79−3.94 (m, 2H). 13C NMR (100 MHz,
CDCl3): δ 13.9, 22.5, 26.1, 27.8, 30.5, 31.6, 55.0, 56.8, 60.7.
In summary, we found that 3,4-epoxy alcohols can be
effectively prepared by MTO-catalyzed epoxidation of homo-
allylic alcohols with hydrogen peroxide as the terminal oxidant.
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Note
3-Methyl-3,4-epoxy-1-butanol (2g).12b,c,16 1H NMR (400
MHz, CDCl3): δ 1.38 (s, 3H), 1.82−1.99 (m, 2H), 2.45 (br, 1H,
OH), 2.64 (d, J = 4.6 Hz, 1H), 2.81 (d, J = 4.6 Hz, 1H), 3.66−3.79 (m,
2H); 13C NMR (100 MHz, CDCl3): δ 21.8, 37.7, 53.0, 56.4, 59.1.
1,2-Epoxy-p-menthan-4-ol (2h).20 A 50 mL flask equipped with
a stirbar was charged with CH2Cl2 (5 mL), ( )-terpinen-4-ol 1h
(1.54g, 10 mmol), 3-methylpyrazole (81 μL, 1.0 mmol, 10 mol %), 1-
methylimidazole (8 μL, 0.1 mmol, 1 mol %), and MTO (2.5 mg, 0.010
mmol, 0.1 mol %). The mixture was cooled to 10 °C by immersing in
a temperature-controlled water bath. H2O2 (35%, 1.01 mL, 12 mmol)
was added all at once to the stirring solution. The resulting two-phase
mixture was stirred vigorously at 10 °C. The disappearance of 1h was
confirmed by GC analysis of small aliquots of the organic phase after 1
h. The reaction mixture was poured into brine and extracted with
CH2Cl2. The organic layer was washed successively with brine and
aqueous Na2S2O3, and then dried over anhydrous Na2SO4. The
solvent of the organic layer was removed out using an evaporator, and
the oily residue obtained was dried under vacuum. 1,2-Epoxy-p-
menthan-4-ol 2h (1.63g, 96% yield, 95% purity by GC) was obtained
as colorless oil. The cis/trans ratio was 88/12, which was determined
by GC. The NMR signals of cis- and trans-isomers were identified
using the cis-isomer prepared according to the literature method.17
confirmed by GC analysis after 2 h. The ratio of epoxide 2h/triol 3
was 96.5/3.5 by a GC peak area ratio at this stage. The reaction
mixture solidified after standing the mixture at room temperature for
one night. Dichloromethane was added to the mixture, and insoluble
white product was collected by filtration and then washed with ethyl
acetate. The obtained white solid was recrystallized from ethyl acetate
to give p-menthane-1,2,4-triol 3 (1.57g, 42%) as white prisms, mp
171−172 °C (lit.21 mp 173 °C). H NMR (400 MHz, DMSO-d6): δ
1
0.81 (d, J = 6.9 Hz, 6H), 1.10 (s, 3H), 1.19−1.31 (m, 2H), 1.35−1.52
(m, 2H), 1.59−1.81 (m, 3H), 3.32−3.37 (m, 1H), 4.22 (s, 1H, OH),
4.60 (s, 1H, OH), 5.17 (d, J = 6.9 Hz, 1H, OH). 13C NMR (100 MHz,
DMSO-d6): δ 16.9, 17.0, 27.1, 29.3, 29.6, 34.0, 37.4, 70.0, 73.3, 73.9.
Procedure for Epoxidation of 6-Methyl-1-hepten-4-ol (1j)
(Table 2, entry 12, Isolated Yield). A 50 mL flask equipped with a
stirbar was charged with CH2Cl2, 6-methyl-1-hepten-4-ol 1j (1.92 g,
15.0 mmol, >99% purity by GC), and 3-methylpyrazole (0.121 mL, 1.5
mmol, 10 mol %). The temperature of the flask was adjusted to 20 °C
by applying an external water bath. MTO (37.4 mg, 0.15 mmol, 1 mol
%) was added to the solution, and then H2O2 (35%, 1.9 mL, 23 mmol)
was added all at once to the stirring solution. The resulting two-phase
mixture was stirred vigorously at 20 °C. After 8 h, the reaction mixture
was poured into brine, and the organic layer was washed successively
with brine (2 times) and an aqueous solution of Na2S2O3. Then the
organic layer was washed with an aqueous solution of tartaric acid (0.5
g in 20 mL of H2O) to remove 3-methylpyrazole, followed with an
aqueous solution of NaHCO3. The organic layer was dried over
anhydrous Na2SO4, and CH2Cl2 was distilled out by an evaporator.
The residual orange oil was dried under vacuum to give crude 1,2-
epoxy-6-methyl-4-heptanol 2j (1.91 g). Kugelrohr distillation of the
crude product under reduced pressure (5 Torr, 100−105 °C) afforded
pure 1,2-epoxy-6-methyl-4-heptanol 2j as colorless oil (1.67 g, 77%
yield, >99% purity by GC).
1
Most of the signals of cis- and trans-isomers in H NMR overlapped.
1H NMR (400 MHz, CDCl3): (cis/trans mixture) δ 0.86−0.95 (m,
6H), 1.30−1.42 (m, 1H), 1.36 (s, 1H), 1.49−1.66 (m, 2H), 1.79−1.93
(m, 2H), 2.00−2.09 (m, 1H), 2.12−2.24 (m, 1H), 2.98 (trans-C2, d, J
= 5.0 Hz), 3.20−3.23 (cis-C2, m, 1H total of cis and trans), 3.53 (s, 1H,
OH). 13C NMR (100 MHz, CDCl3): (cis) δ 16.5, 16.7, 23.8, 25.7,
29.3, 31.8, 36.8, 58.6, 62.0, 71.8; (trans) δ 16.6, 16.7, 22.8, 25.3, 27.4,
33.1, 38.3, 57.7, 57.7, 70.6.
1-Phenyl-3,4-epoxy-1-butanol (2i). Colorless oil. The cis/trans
1
ratio was approximately 50/50, which was determined by H NMR
integration of protons at C1. The NMR signals of cis- and trans-
isomers were determined using cis-rich mixture (cis/trans = 64/36)
that was prepared according to the literature method.17 1H NMR (400
MHz, CDCl3): (cis/trans mixture) δ 1.72−2.15 (m, 2H), 2.45−2.49
(cis-C1, m), 2.55−2.59 (trans-C1, m, 1H total of cis and trans), 2.70−
2.82 (cis- and trans-C2, m, 2H, overlap OH proton), 2.94−3.00 (cis-
C1, m), 3.11−3.17 (trans-C1, m, 1H total of cis and trans), 4.87−4.93
(m, 1H), 7.24−7.40 (m, 5H). 13C NMR (100 MHz, CDCl3): (cis) δ
41.7, 46.7, 50.2, 72.6, 125.7, 127.6, 128.4, 143.7; (trans) δ 41.3, 47.1,
49.9, 71.6, 125.5, 127.5, 128.4, 144.0. Anal. Calcd for C10H12O2: C,
73.15; H, 7.37. Found: C, 72.94; H, 7.35.
Procedure for 10 g Scale Epoxidation of cis-3-Octen-1-ol
(1e) (Table 2, entry 4). A 100 mL flask equipped with a stirbar and
thermometer was charged with cis-3-octen-1-ol 1e (10 g, 78.0 mmol,
>97% purity by GC) and 3-methylpyrazole (0.63 mL, 7.8 mmol, 10
mol %). The flask was cooled to 10 °C by applying an external cooling
bath. MTO (19.4 mg, 0.078 mmol, 0.1 mol %) was added to the
solution, and then H2O2 (35%, 7.9 mL, 94 mmol) was added dropwise
to the stirring solution from a dropping funnel (ca. 20 min). During
the H2O2 addition, the temperature of the solution was kept below 27
°C. The resulting two-phase mixture was stirred vigorously at 10 °C.
The reaction was completed after 2 h, and CH2Cl2 was added to the
reaction mixture. The organic layer of the reaction mixture was washed
successively with brine (2 times) and with an aqueous solution of
Na2S2O3. Then the organic layer was washed with an aqueous solution
of tartaric acid (2.5 g in 25 mL of H2O) to remove 3-methylpyrazole
completely, followed with an aqueous solution of NaHCO3. The
organic layer was dried over anhydrous Na2SO4, and CH2Cl2 was
distilled out by an evaporator. The residual yellow oil was dried under
vacuum to give crude cis-3,4-epoxy-1-octanol 2e (11.2 g). Distillation
of the crude product under reduced pressure (4 Torr, 106−107 °C)
afforded cis-3,4-epoxy-1-octanol 2e as colorless oil (9.6 g, 85% yield,
>97% purity by GC).
1,2-Epoxy-6-methyl-4-heptanol (2j). Colorless oil. The cis/trans
ratio was 50/50, which was determined by GC by using GL Sciences
InertCap WAX column (30 m length × 0.25 mm i.d., 0.25 μm film
thickness). The NMR signals of cis- and trans-isomers were
determined using a cis-rich mixture (cis/trans = 68/32) that was
prepared according to the literature method.17 1H NMR (400 MHz,
CDCl3): (cis/trans mixture) δ 0.88−0.97 (m, 6H), 1.21−1.31 (m, 1H),
1.43−1.62 (m, 2H), 1.72−1.87 (m, 2H), 2.14 (br, 1H, OH), 2.49−
2.53 (cis-C1, m), 2.59−2.64 (trans-C1, m, 1H total of cis and trans),
2.77−2.81 (cis-C2, m), 2.81−2.86 (trans-C2, m, 1H total of cis and
trans), 3.07−3.13 (cis-C1, m), 3.13−3.19 (trans-C1, m, 1H total of cis
and trans), 3.86−4.02 (m, 1H). 13C NMR (100 MHz, CDCl3): (cis) δ
21.9, 23.2, 24.3, 40.2, 46.5, 46.5, 50.4, 68.1; (trans) δ21.9, 23.2, 24.3,
39.7, 46.6, 46.9, 50.1, 67.0. Anal. Calcd for C8H16O2: C, 66.63; H,
11.18. Found: C, 66.23; H, 10.90.
ASSOCIATED CONTENT
■
S
* Supporting Information
3,4-Epoxy-1-butanol (2k).12b,c 1H NMR (400 MHz, CDCl3): δ
1.64−1.74 (m, 1H), 1.88−1.98 (m, 1H), 2.56−2.60 (m, 1H), 2.81 (t, J
= 4.3 Hz, 1H), 3.07−3.12 (m, 1H), 3.59 (s, 1H, OH), 3.74−3.81 (m,
2H). 13C NMR (100 MHz, CDCl3): δ 34.7, 46.6, 50.2, 59.2.
Determination of cis/trans ratio of epoxides, 2h, 2i, and 2j, and
1H and 13C NMR spectra of 2a, 2b, 2d−k, and 3. This material
is available free of charge via the Internet at http://pubs.acs.org.
p-Menthane-1,2,4-triol (3). Isolation of Byproduct on
( )-Terpinen-4-ol (1h) Epoxidation. A 50 mL flask equipped
with a stirbar was charged with ( )-terpinen-4-ol 1h (3.09 g, 20
mmol), 3-methylpyrazole (161 μL, 2.0 mmol, 10 mol %), and MTO
(10 mg, 0.040 mmol, 0.2 mol %). The mixture was cooled to 10 °C by
immersing in a temperature-controlled water bath. H2O2 (35%, 2.02
mL, 24 mmol) was added all at once to the stirring solution. The
resulted mixture was stirred at 10 °C. The disappearance of 1h was
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: s-yamazk@itc.pref.toyama.jp.
Notes
The authors declare no competing financial interest.
9887
dx.doi.org/10.1021/jo301825j | J. Org. Chem. 2012, 77, 9884−9888

The Journal of Organic Chemistry
Note
(21) Cristea, I.; Kozma, E.; Batiu, C. Tetrahedron: Asymmetry 2002,
13, 915.
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