Epoxidation of olefins with a silica-supported peracid in supercritical carbon dioxide under flow conditions

Article abstract of DOI:10.1021/jo300532f

Anhydrous 2-percarboxyethyl-functionalized silica (2b), a recyclable supported peracid, is a suitable reagent to perform the epoxidation of alkenes 1 in supercritical carbon dioxide at 250 bar and 40 °C under flow conditions. This procedure simplifies the isolation of the reaction products and uses only carbon dioxide as a solvent under mild conditions. The solid reagent 2b can be easily recycled by a reaction with 30% hydrogen peroxide in an acid medium.

Full text of DOI:10.1021/jo300532f

Article
pubs.acs.org/joc
Epoxidation of Olefins with a Silica-Supported Peracid in
Supercritical Carbon Dioxide under Flow Conditions
Rossella Mello, Ana Alcalde-Aragones, Andrea Olmos, María Elena Gonzalez-Nunez,*
́
́
́
̃
and Gregorio Asensio
́
Departamento de Quımica Organ
́
ica, Facultad de Farmacia, Universidad de Valencia, Avda. Vicente Andres
́
Estelles
́
s.n.,
46100-Burjassot, Valencia, Spain
S
* Supporting Information
ABSTRACT: Anhydrous 2-percarboxyethyl-functionalized silica (2b), a recyclable
supported peracid, is a suitable reagent to perform the epoxidation of alkenes 1 in
supercritical carbon dioxide at 250 bar and 40 °C under flow conditions. This
procedure simplifies the isolation of the reaction products and uses only carbon
dioxide as a solvent under mild conditions. The solid reagent 2b can be easily recycled
by a reaction with 30% hydrogen peroxide in an acid medium.
This report describes the use of supercritical carbon dioxide
(scCO2) as a reaction medium for the epoxidation of olefins 1
with recyclable 2-percarboxyethyl-functionalized silica (2b)4
under flow conditions. The reaction works efficiently for
simple, substituted olefins 1 and enables good yields of the
corresponding epoxides 3. The procedure described herein
replaces organic solvents with scCO2 and simplifies the isolation
of epoxides 3 to a simple depressurization of the flowing scCO2
solution. The process is not suitable for those olefins 1 carrying
strong H-bond donor/acceptor substituents, such as alkenyl
alcohols. This report also describes an optimized procedure for
the preparation of silica-supported peracid 2b, which avoids the
use of highly concentrated hydrogen peroxide.
INTRODUCTION
■
Epoxides are versatile intermediates in organic synthesis and
important commodity products which are produced at scales
ranging from millions of tons to a few grams per year.1 The
reaction of alkenes 1 with organic peroxyacids 2a (eq 1)2 is still
widely used for the production of epoxides 3 on both the
industrial and laboratory scales, despite certain disadvantages
such as the shock sensitivity of organic peroxyacids 2a, the low
atom economy of the process, the use of chlorinated or
aromatic solvents as a reaction medium, and the formation of 1
equiv of carboxylic acid as a byproduct, which has to be
separated from the acid-sensitive epoxide 3 by neutralization
and extraction with organic solvents.
The synthetic importance of this transformation has
prompted research into alternative methods3 for the safe and
environmentally benign production of epoxides 3 from olefins
1. Use of supported organic peroxyacids4,5 is a suitable
approach to improve the reaction conditions, as immobilization
on solid supports minimizes the risk of explosion of the
peroxide and simplifies the removal of the carboxylic acid from
the reaction products. This process could be further improved
by performing the reaction under flow conditions and by
avoiding the use of chlorinated or aromatic solvents.
Supercritical carbon dioxide (scCO2) is a convenient medium
in which to perform heterogeneous reactions6 with supported
reagents and catalysts under flow conditions, given its
adjustable solvating power, excellent transport properties,
readily accessible critical conditions (Tc = 31.0 °C, Pc = 73.8
bar), benign character, low cost, and the existence of a
technology platform to use scCO2 in large-scale processes.
However, the epoxidation of olefins under flow conditions in
this medium has not been described up to now.
RESULTS AND DISCUSSION
■
2-Percarboxyethyl-functionalized silica (2b)was prepared4,5a,b
by acid hydrolysis of 2-cyanoethyl-functionalized silica,
obtained by a standard sol−gel procedure, followed by
treatment of the resulting 2-carboxyethyl-functionalized silica
with 30% hydrogen peroxide in an acid medium (Scheme 1).
Scheme 1. Synthesis of the Supported Peracid 2b4
The preparation of the silica-supported peracid 2b described
herein (see the Experimental Section) improves upon
previously reported procedures,4,5 which required less available
and hazardous 70% solutions of hydrogen peroxide. Solid
peroxidic reagent 2b was dried under vacuum at room
temperature until a constant weight was achieved. An analysis
1
of the hybrid material by conventional H NMR following a
Received: March 12, 2012
Published: April 25, 2012
© 2012 American Chemical Society
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reported procedure7 and iodometric titration, showed loads of
2.6 mmol of organic ligands and 1.2 mmol of peroxidic ligands
per gram of hybrid material, respectively. Silica-supported
peracid 2b was stored at −20 °C for weeks with no noticeable
loss of peroxidic titer.
Table 1. Oxidation of Alkenes 1 with [SiO2]-
CH2CH2COOOH (2b) in scCO2 under Flow Conditions
a
Oxidations were carried out by flowing scCO2 (0.10−0.12
mL scCO2 min−1) at 250 bar and 40 °C for 2 h through the
loop of a Rheodyne valve containing substrate 1 and then
through a column packed with anhydrous reagent 2b (initial
molar ratios alkene 1:peracid 2b 1:2 or 1:3) (eq 2). The system
was depressurized through a micrometric valve, and the
reaction product was collected in a trap cooled to −78 °C.
The residue, which was obtained after gently heating the trap,
was dissolved in dichloromethane and analyzed by gas
chromatography. The reaction products were identified by
1
gas chromatography/mass spectrometry and by H and 13C
NMR analyses. The results are shown in Table 1.
The silica-supported reagent recovered from the column was
white and had a loose appearance in all cases. Iodometric
titration of the consumed reagent showed loss of peroxidic titer,
which corresponded to the oxygen transfer performed on the
substrate. The mass balances for alkenes 1a−l, which were
determined by carrying out the reactions in the presence of
adamantane as an internal standard, were correct in all cases,
indicating that the silica surface did not retain the
corresponding epoxides 3a−l under these conditions. Silica-
supported peracid 2b was recycled by treating the consumed
solid material with 30% hydrogen peroxide in an acid medium,
following the procedure described in the Experimental Section.
After five cycles, the load of peroxidic ligands on the silica
surface was 0.8 mmol per gram of hybrid material, indicating a
loss of ca. 30% of organic ligands.
a
The results reveal that 2-percarboxyethyl-functionalized silica
(2b)4 is a superior reagent for the epoxidation of simple,
substituted olefins 1 in scCO2 under flow conditions (Table 1).
One interesting improvement in relation to reactions with
soluble peracids is that epoxides 3 (Table 1) did not undergo
acid-catalyzed side reactions promoted by the acidic silanol and
carboxylic acid groups covering the silica surface. This result is
most significant, as it is known that scCO2’s low solvating ability
enhances acid−base interactions.6 A key factor for the success
of the reaction was the anhydrous character of the supported
peracid 2b. The use of 20−25% hydrated silica-supported
peracid 2b led to low substrate conversions and extensive ring
opening of epoxides 3 in all cases. These results indicate that
the hydration layer on the silica surface poses a barrier for the
interation of hydrophobic substrates 1 with the surface
peroxidic moieties and that the water molecules coordinated
to the surface silanol and carboxylic acid groups are sufficiently
nucleophilic to perform the acid-catalyzed ring opening of
epoxides 3. The control experiments carried out with an initial
2:1 molar ratio of cyclohexene (1a) to peracid 2b led to the
complete consumption of the peracid 2b, demonstrating that
the high diffusivity and low viscosity of scCO2 allow the
substrate to reach all the peroxidic ligands on the silica surface.
Reactions in scCO2 at 250 bar, 40 °C and flow rate 0.11−0.12 mL
scCO2 min−1, with anhydrous 2b (1.2 mmol of peracid g−1), and molar
ratio alkene 1:peracid 2b 1:2. Substrate conversion was complete in all
b
the cases except where noted. Determined by GC analysis of the
c
reaction mixtures; mass balance >98% in all the cases. Initial molar
d
e
ratio alkene 1:peracid 2b 1:3. Syn:anti ratio 50:50.
Substrate
conversion <10%.
The results provided in Table 1 evidence the distinct
reactivity of olefins 1 toward electrophilic oxidant 2b.8 Thus,
the quantitative epoxidation of terminal olefins 3-phenyl-
propene (1f) and 1-hexene (1g) (entries 6 and 7, Table 1)
required a 3-fold excess of peracid 2b, while a 2-fold excess
sufficed for the internal olefins cyclohexene (1a) and 3-heptene
(1b,c) (entries 1−3, Table 1). Electron-withdrawing sub-
stituents deactivate the CC double bond toward the
electrophilic oxidant,8 and accordingly, trans-2-hexenyl acetate
(1j) and 2-cyclohexenylacetate (1l) required 3 equiv of peracid
2b (entries 10 and 12, Table 1) to quantitatively convert them
into the corresponding epoxides 3. However, 2 equiv of peracid
2b sufficed for 3-cyclohexenylmethyl acetate (1h) and methyl
2-cyclohexenylcarboxylate (1i) (entries 8 and 9, Table 1), since
the longer distance between the functional groups in the former
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and the weaker electron-withdrawing effect of the substituent in
the latter render the CC double bond less deactivated.
The acidic character of the silica surface became evident for
highly acid-sensitive epoxides 3. For instance, styrene (1m)
failed to give the corresponding epoxide 3m under our reaction
conditions. In this instance, the reaction afforded a complex
mixture of products which remained adsorbed on the silica
surface. This result was attributed to the acid sensitivity of
styrene oxide (3m) and the overoxidation of the rearranged
products. Substrate conversion was very poor in this case
(<10%) due to depletion of peroxidic ligands in the oxidative
side processes and the low reactivity of styrene.
Table 2. Oxidation of Alkenes 1 with [SiO2]-
CH2CH2COOOH (2b) in scCO2 in Batch Mode
a
The presence of strong H-bond donor/acceptor substituents
in olefin 1 did not interfere with the epoxidation reaction but
led to the strong adsorption of the corresponding epoxide 3 on
the silica surface. For instance, epoxidation of 2-cyclohexen-1-ol
(1n) with a 3-fold excess of peracid 2b led to its quantitative
conversion into epoxide 3n under our experimental conditions
(eq 3). The reaction product had to be recovered by either
a
Reactions in scCO2 at 250 bar, 40 °C, with anhydrous 2b (1.2 mmol
of peracid g−1) and molar ratio alkene 1:peracid 2b 1:1 for 90 min.
The reaction product was extracted with scCO2 at a flow rate of 0.11−
b
0.12 mL of scCO2 min−1. Epoxides 3 were the only products (yield
c
>99%), except where indicated. Determined by GC analysis of the
d
reaction mixtures; mass balance >98% in all cases. Products derived
from acid-catalyzed side reactions were isolated from the solid reagent.
flowing a solution of ethyl acetate in scCO2 at 250 bar and 40
°C through the solid reagent or thoroughly washing it with
dichloromethane once the system was depressurized. The
oxygen transfer reaction took place exclusively on the syn
diastereoface of the CC double bond, which is in agreement
with the directing effect reported for the hydroxyl groups in the
epoxidation of allylic and homoallylic alcohols with organic
peracids under homogeneous conditions.9 Conversely, epox-
idation of the substituted cyclic olefins 1h,i,l gave 50:50
mixtures of the syn and anti diastereomers (entries 8, 9, and 12,
Table 1).
convenient approach to achieve the quantitative conversion of
the less reactive olefins 1 than prolonging the reaction time.
Use of anhydrous silica-supported potassium peroxomono-
sulfate, KHSO5,5 a much stronger electrophilic oxidant than
organic peracids, for the epoxidation of the less reactive olefins
1 did not improve reaction efficiency, as the strongly acidic
character of the silica surface, which is covered by the KHSO4
species from the Caroate triple salt used for preparing the
reagent and generated in the oxygen transfer reaction,
promoted extensive acid-catalyzed side reactions of epoxides
3 and the overoxidation of the rearranged products.
The reactions required an excess of oxidant 2b to achieve the
complete conversion of substrates 1 (Table 1). This result can
be attributed to the short contact time of the substrate with the
supported reagent under the flow conditions (ca. 21 min under
our reaction conditions). Control experiments carried out in
batch mode for longer reaction periods improved the
performance of the solid peracid 2b, leading to good
conversions of substrates despite the system’s static character
(Table 2). These reactions were carried out at 250 bar and 40
°C with an initial 1:1 molar ratio of alkene 1 and peracid 2b by
pressurizing with CO2 a thermostated reactor containing the
solid reagent through a Rheodyne valve loaded with the
substrate, allowing the system to stand for 90 min, and then
flowing scCO2 at 250 bar and 40 °C for 2 h to collect the
reaction products in a cooled trap. Substrate conversions were
lower for terminal olefin 1g and alkenyl esters 1j,k (entries 4−
6, Table 2) than for internal olefins 1a,b,d (entries 1−3, Table
2), in agreement with the distinct reactivity of olefins 1 toward
electrophilic oxidant 2b. Mass balances were correct in all cases
except for the most reactive olefin 1d which, under these
conditions, led to a mixture of products derived from the acid-
catalyzed reactions of epoxide 3d and to the overoxidation of
the rearranged products. The organic material remained
adsorbed on the solid reagent and was recovered by thoroughly
washing it with methanol. This result indicates that using an
excess of anhydrous solid peracid 2b proves to be a more
CONCLUSIONS
■
2-Percarboxyethyl-functionalized silica (2b) is a suitable reagent
to perform the epoxidation of alkenes 1 in supercritical carbon
dioxide at 250 bar and 40 °C under flow conditions. Epoxides 3
undergo neither acid-catalyzed ring opening nor any other side
reactions under these conditions, provided that the supported
peracid 2b is anhydrous. The reaction is not suitable for those
alkenes 1 carrying strong H-bond donor/acceptor substituents,
such as hydroxyl groups. This procedure uses only carbon
dioxide as a solvent under mild conditions and simplifies both
the isolation of the reaction products and the recovery of the
carboxylic acid. Solid reagent 2b can be easily recycled by a
reaction with 30% hydrogen peroxide in an acid medium.
EXPERIMENTAL SECTION
Caution! The experiments described in this paper involve the use of
relatively high pressures and require equipment with the appropriate
pressure rating.
General Considerations. Reagents and solvents were purified
following standard procedures.10 The glassware used in the reactions
with hydrogen peroxide was carefully cleaned and washed before use
with a solution of EDTA in ultrapure water (0.25 g L−1) to remove any
traces of metals. Hydration of silica-supported peracid 2b was
performed by adding the desired amount of water at room
temperature to the anhydrous material and stirring for 6 h in a closed
■
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vial. The high-pressure equipment consisted of a 250 mL AISI 316
stainless steel jacketed autoclave, a diaphragm pump (Orlita MHS 30/
8) with a maximum theoretical flow of 8.44 L/h of liquid CO2, a set of
high-pressure valves, pressure and temperature probes, and security
rupture disks suitably placed to control the flow of CO2 along the
system.
2-Percarboxyethyl-Functionalized Silica (2b). A suspension of
3 g of 2-carboxyethyl-functionalized silica (2.6 mmol g−1) in 7.5 mL of
70% H2SO4 was stirred at 5 °C for 30 min. Then, 2.5 mL of 30%
hydrogen peroxide was added at once and the mixture was allowed to
react at 0 °C with stirring for 6 h. The solid was filtered and washed
with cold doubly distilled water until the filtrate showed a negative
peroxide test. The solid was dried under vacuum at room temperature
until constant weight. Standard iodometric titration determined a
peroxide content of 1.2 mmol per gram of material.
36.6, 51.5. EM (EI+, 70 eV; m/z (rel abund)): 54 (42), 67 (37), 79
(75), 81 (100), 95 (17), 109 (5), 110 (3, [M•+]).
1
2-Phenylpropene Oxide (3f) [4436-24-2]. H NMR (300 MHz,
CDCl3): δ 2.5 (1H, dd, J1 = 2.7 Hz, J2 = 5.0 Hz), 2.7−2.9 (3H, m), 3.1
(1H, dsext, J1 = 2.7 Hz, J2 = 3.9 Hz, J3 = J4 = 5.5 Hz), 7.1−7.2 (5H, m).
13C NMR (75 MHz, CDCl3): δ 38.6, 46.7, 52.3, 126.5, 128.4, 128.8,
137.0. EM (EI+, 70 eV; m/z (rel abund)): 44 (30), 50 (12), 65 (25),
78 (21), 91 (100), 104 (35), 117 (13), 134 (55, [M•+]).
1
1-Hexene Oxide (3g) [592-41-6]. H NMR (300 MHz, CDCl3): δ
0.9 (3H, t, J = 7 Hz), 1.3−1.6 (6H, m), 2.5 (1H, dd, J1 = 2.8 Hz, J2 =
4.9 Hz), 2.8 (1H, dd, J1 = 4.1 Hz, J2 = 4.9 Hz), 2.9 (1H, d sext, J1 = 2.8
Hz, J2 = 4.0 Hz, J3 = J4 = 5.5 Hz). 13C NMR (75 MHz, CDCl3): δ 13.9,
22.4, 28.0, 32.0, 47.3, 52.7. EM (EI+, 70 eV; m/z (rel abund)): 39
(18), 41 (42), 42 (43), 55 (39), 58 (33), 71 (100), 85 (7), 99 (1), 100
(0, [M•+]).
Oxidation of Alkenes with Silica-Supported Peracid 2b in
scCO2. General Procedure. A stainless steel 8 mm i.d. column was
packed with 1.35 g of silica-supported peracid 2b (1.2 mmol g−1, 2
equiv) and tightly closed with two filters placed on either end of the
column to prevent any displacement of the solid reagent throughout
the experiment. The column outlet was connected to a high-pressure
1-Methylcarbonyloxymethyl-3-cyclohexene Oxide (3h) [75228-
31-8]. Mixture of isomers 50:50. 1H NMR (300 MHz, CDCl3): δ 0.9−
1.2 (1.30 H, m), 1.3−1.9 (5H, m), 2.0−2.1 (4.5H, s), 2.1−2.2 (1.1H,
m), 3.1−3.2 (2H, m), 3.82 (1H, d, J = 6.0 Hz), 3.86 (1H, dd, J1 = 2.2
Hz, J2 = 6.5 Hz). 13C NMR (75 MHz, CDCl3): δ 20.8, 21.0, 22.8, 23.6,
24.5, 27.0, 28.1, 29.3, 32.1, 51.0, 51.6, 52.3, 52.4, 68.3, 68.5, 171.07,
171.09. EM (EI+, 70 eV; m/z (rel abund)): isomer 1, 43 (100), 55
(22), 67 (44), 81 (85), 95 (33), 110 (39), 127 (26), 170 (0, [M•+]);
isomer 2, 43 (100), 55 (21), 67 (43), 81 (81), 95 (37), 110 (43), 127
(23), 170 (0, [M•+]).
micrometric valve which was connected to a trap cooled with a dry ice
1
bath through a
/ in. Teflon tube. The pressure in the trap was
8
equilibrated with a flow of nitrogen. The 250 mL autoclave set at 40
°C was connected to the column inlet by a Rheodyne valve. The
autoclave was charged with CO2 and pressurized to 250 bar. Then
both the loop of the Rheodyne valve and the column were placed in a
water bath heated to 40 °C, and the system was pressurized by
carefully opening the inlet valve. The stroke volume of the pump and
the aperture of the high-pressure micrometric outlet valve were
regulated to achieve steady continuous-flow conditions at 250 bar. The
CO2 flow at the system outlet was monitored with a bubble flow
meter. The Rheodyne valve was loaded with 82 μL (0.8 mmol) of
cyclohexene (1a), which was then injected into the system once the
work regime had been achieved. The system was left to operate for 2 h.
The inlet valve was then closed and the system was depressurized. The
trap was warmed to room temperature, and the colorless residue was
dissolved in deuterated chloroform and analyzed with the aid of GC,
1-Methoxycarbonyl-2-cyclohexene Oxide (3i) [864724-47-0].
1
Mixture of isomers 60:40. H NMR (300 MHz, CDCl3): δ 1.3−1.4
(1.2H, m), 1.5−1.6 (1.4H, m), 1.6−2.0 (5.4H, m), 2.0−2.2 (3.8H, m),
2.4−2.5 (1H,m), 3.0−3.1 (2.3H, m), 3.1−3.2 (1H, m), 3.60 (1.9H, s),
3.61 (3H, s). 13C NMR (75 MHz, CDCl3): major isomer, δ 22.7, 22.8,
27.1, 35.6, 51.6, 51.7, 52.1, 175.8; minor isomer, δ 20.9, 23.9, 26.2,
37.7, 50.6, 51.3, 51.7, 52.1, 175.2. EM (EI+, 70 eV; m/z (rel abund));
major isomer, 67 (27), 70 (28), 79 (30), 87 (19), 97 (100), 100 (24),
113 (7), 125 (26), 128 (7), 137 (3), 156 (0.5, [M•+]); minor isomer,
67 (26), 70 (29), 81 (41), 87 (19), 97 (100), 100(21), 113 (7), 128
(6), 141 (1), 156 (0.7, [M•+]).
(E)-1-Methylcarbonyloxy-2-hexene Oxide (3j) [92315-15-6]. 1H
NMR (CDCl3) δ 0.9 (3H, t, J = 7.3 Hz), 1.3−1.5 (4H, m), 2.0 (3H, s),
2.8 (1H, m), 2.9 (1H, m), 3.8 (1H, dd, J1 = 6.3 Hz, J2 = 12.2 Hz), 4.3
(1H, dd, J1 = 3.1 Hz, J2 = 12.2 Hz). 13C NMR (75 MHz, CDCl3): δ
13.7, 19.0, 20.6, 33.3, 55.0, 56.2, 64.6, 170.6. EM (EI+, 70 eV; m/z (rel
abund)): 43 (100), 55 (11), 57 (8), 73 (3), 86 (6), 99 (1), 115 (9),
129 (1), 158 (0, [M•+]).
1
GC-MS, H, and 13C NMR techniques. The solid reagent recovered
from the column was washed four times with 15 mL of dichloro-
methane in a round-bottomed flask with magnetic stirring. The filtered
solution was analyzed by means of GC and then evaporated under
vacuum at 0 °C.
Cyclohexene Oxide (3a) [286-20-4]. 1H NMR (300 MHz, CDCl3):
δ 1.1−1.3 (2H, m), 1.4−1.5 (2H, m), 1.7−1.9 (2H, m), 1.9−2.0 (2H,
m), 3.1 (2H, m). 13C NMR (75 MHz, CDCl3): δ 19.4, 24.4, 52.2. EM
(EI+, 70 eV; m/z (rel abund)); 39 (33), 41 (50), 42 (47), 54 (35), 55
(31), 57 (24), 69 (27), 70 (18), 83 (100), 97 (15), 98 (4, [M•+]).
(E)-3-Heptene Oxide (3c) [56052-95-0]. 1H NMR (300 MHz,
CDCl3): δ 0.92 (3H, dt, J1 = 2,6 Hz, J2 = unresolved), 0.95 (3H, t, J =
7.5 Hz), 1.3−1.6 (6H, m), 2.6−2.7 (2H, m). 13C NMR (75 MHz,
CDCl3): δ 9.8, 13.8, 19.3, 25.1, 34.0, 58.5, 60.0. EM (EI+, 70 eV; m/z
(rel abund)): 57 (100), 67 (14), 72 (90), 81 (4), 85 (37), 99 (14), 114
(1, [M•+]).
1-Methylcarbonyloxy-5-hexene Oxide (3k) [107127-73-1]. 1H
NMR (300 MHz, CDCl3): δ 1.4−1.7 (6H, m), 2.0 (3H, s), 2.4 (1H,
ddd, J1 = 0.9 Hz, J2 = 2.7 Hz, J3 = 4.9 Hz), 2.7 (1H, ddd, J1 = 0.9 Hz, J2
= 4.5 Hz, J3 = 4.5 Hz), 2.8−2.9 (1H, m), 4.0 (2H, td, J1 = 0.81 Hz, J2 =
6.43 Hz). 13C NMR (75 MHz, CDCl3): δ 20.9, 22.4, 28.3, 32.0, 46.9,
52.0, 64.2, 171.1. EM (EI+, 70 eV; m/z (rel abund)): 43 (100), 55
(20), 67 (39), 85 (50), 97 (32), 115 (1), 158 (0, [M•+]).
1-Methylcarbonyloxy-2-cyclohexene Oxide (3l) [84414-68-6].
1
Mixture of isomers 60:40. H NMR (300 MHz, CDCl3): δ 1.1−1.6
(6.7H, m), 1.7−1.9 (4H, m), 1.9−2.0 (1.5H, m), 2.1 (5.2H, ds), 3.0
(1H, d, J = 3.6 Hz), 3.1−3.2 (1H, m), 3.2−3.3 (1.3H, m), 5.0(1H, t, J
= 7 Hz), 5.1 (1H, ddd, J1 = 1.7 Hz, J2 = 5.1 Hz, J3 = 9.1 Hz). 13C NMR
(75 MHz, CDCl3): major isomer, δ 14.4, 21.1, 23.6, 25.7, 52.5, 53.3,
68.0, 170.1; minor isomer, δ 19.3, 21.1, 22.5, 24.4, 52.8, 54.2, 70.8,
170.8. EM (EI+, 70 eV; m/z (rel abund0): major isomer, 43 (100), 55
(18), 68 (18), 70 (54), 86 (9), 96 (17), 112 (21), 156 (0, [M•+]);
minor isomer, 43 (100), 55 (14), 67 (18), 70 (61), 86 (5), 96 (19),
112 (24), 156 (0, [M•+]).
(Z)-3-Heptene Oxide (3b) [56052-94-9]. 1H NMR (300 MHz,
CDCl3): δ 1.0−1.2 (m, 6H), 1.4−1.7 (m, 6H), 2.8−3.0 (2H, m); 13C
NMR (75 MHz, CDCl3): δ 10.5, 14.0, 19,8, 21.0, 29.6, 57.3, 58.5. EM
(EI+, 70 eV; m/z (rel abund)): 57 (100), 67 (14), 72 (87), 81 (3), 85
(41), 99 (13), 114 (1, [M•+]).
(Z)-3-Methylpentene Oxide (3d) [1447-39-8]. 1H NMR (300
MHz, CDCl3): δ 0.9 (3H, t, J = 7.5 Hz), 1.2 (3H, s), 1.3 (3H, d, J =
5.5 Hz), 1.5 (1H, dq, J1 = 7.5 Hz, J2 = 13.8 Hz), 1.6 (1H, dq, J1 = 7.5
Hz, J2 = 13.8 Hz), 2.9 (1H, q, J = 5.5 Hz). 13C NMR (75 MHz,
CDCl3): δ 9.2, 14.1, 15.8, 31.3, 59.0, 62.0. EM (EI+, 70 eV; m/z (rel
abund)): 41 (100), 43 (63), 45 (22), 56 (47), 72 (71), 85 (2), 100 (1,
[M•+]).
1
1-Hydroxy-2-cyclohexene Oxide (3n) [1192-78-5]. H NMR (300
MHz, CDCl3): δ 1.2−1.3 (2H, m), 1.4−1.6 (2H, m), 1.7−1.9 (2H,
m), 2.0 (1H, broad s, OH), 3.3−3.4 (2H, m), 4.0 (1H, ddd, J1 = 2.9
Hz, J2 = 4.7 Hz, J3 = 7.4 Hz). 13C NMR (75 MHz, CDCl3): δ 18.1,
23.1, 28.9, 55.3, 55.4, 67.0. EM (EI+, 70 eV; m/z (rel abund)): 41
(20), 57 (74), 58 (37), 60 (7), 70 (100), 83 (4), 95 (6), 114 (0,
[M•+]).
exo-Norbornene Oxide (3e) [3146-39-2]. 1H NMR (300 MHz,
CDCl3): δ 0.7 (1H, d), 1.1−1.2 (2H, m), 1.3 (1H, m), 1.4 (2H, m),
2.4 (2H, s), 3.1 (2H, s). 13C NMR (75 MHz, CDCl3): δ 25.0, 26.2,
4709
dx.doi.org/10.1021/jo300532f | J. Org. Chem. 2012, 77, 4706−4710

The Journal of Organic Chemistry
Article
(8) (a) Sharpless, K. B.; Verhoeven, T. R. Aldrichim. Acta 1979, 12,
63−73. (b) Stumpf, W.; Rombusch, K. Justus Liebigs Ann. Chem 1965,
687, 136−199. (c) Swern, D. Org. React. 1953, 7, 378−433.
ASSOCIATED CONTENT
■
S
* Supporting Information
Figures giving 1H and 13C NMR spectra for the reaction
products. This material is available free of charge via the
Internet at http://pubs.acs.org.
́
(9) (a) Bach, R. D.; Estevez, C. M.; Winter, J. E.; Glukhovtsev, M. N.
J. Am. Chem. Soc. 1998, 120, 680−685. (b) Hoveyda, A. H.; Evans, D.
A.; Fu, G. C. Chem. Rev. 1993, 93, 1307−1370.
(10) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory
Chemicals, 3rd ed.; Pergamon: New York, 1988.
AUTHOR INFORMATION
Corresponding Author
*E-mail: elena.gonzalez@uv.es
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
Financial support from the Spanish Direccion
■
́
General de
Investigacion
́
(CTQ2010-21172, CTQ2007-65251/BQU, and
CTQ2007-30762-E) and Consolider Ingenio 2010 (CSD2007-
00006), is gratefully acknowledged. A.A.-A. and A.O. thank the
́
Spanish Ministerio de Educacion y Ciencia for fellowships. We
́
thank Solvay Quimica SL for a generous gift of hydrogen
peroxide. We also thank the SCSIE (Universidad de Valencia)
for their instrumental facilities.
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