Org. Synth. 2002, 78, 225
DOI: 10.15227/orgsyn.078.0225
IN SITU CATALYTIC EPOXIDATION OF OLEFINS WITH TETRAHYDROTHIOPYRAN-4-ONE
AND OXONE: trans-2-METHYL-2,3-DIPHENYLOXIRANE
[
Oxirane, 2-methyl-2.3-diphenyl-, trans-
]
Submitted by Dan Yang, Yiu-Chung Yip, Guan-Sheng Jiao, and Man-Kin Wong
1
.
Checked by Jason M. Diffendal and Rick L. Danheiser.
1. Procedure
Caution! This procedure should be conducted in an efficient fume hood to
assure the adequate removal of oxygen.
A 250-mL, round-bottomed flask equipped with a Teflon-coated
magnetic stirring bar is charged with
3.89
g (20.0 mmol) of trans-α-methylstilbene
(Note 1),
0.12 g (1.0
mmol) of tetrahydrothiopyran-4-one
(Note 2),
90 mL of acetonitrile
(Note 3) and
60 mL
of aqueous 4 × 10−4 M ethylenediaminetetraacetic acid,
disodium salt (Na2·EDTA) solution (Note 4).
To this stirred mixture is added in portions a mixture of
18.4
g (30.0 mmol) of Oxone
®
(Note 5) and
7.8 g (93
mmol) of sodium bicarbonate
over a period
of 3 hr at room temperature. A slow evolution of gas bubbles is observed (Note 6). The reaction is complete in 3.5 hr as shown by TLC analysis
(Note 7). The contents of the flask are poured into a 250-mL
separating funnel and extracted with three
50-mL
portions of ethyl acetate
. The combined organic layers
are washed with
25 mL of saturated sodium
chloride (NaCl) solution, dried over anhydrous
magnesium sulfate
, filtered, and concentrated under
reduced pressure. The residue is purified by flash column chromatography (Note 8) to afford 4.10-4.18
g (98-99%) of
2-methyl-2,3-diphenyloxirane
as a colorless oil that solidifies on standing to a white solid (Note 9).
2. Notes
1.
trans-α-Methylstilbene
was purchased from Aldrich Chemical Company, Inc.
and used without further purification.
2.
Tetrahydrothiopyran-4-one
was purchased from Acros Chemical Company, Inc.
and
used without further purification.
Oxone
®
rapidly converts this ketone to
1,1-dioxotetrahydrothiopyran-4-one
,
which functions as the catalyst for the epoxidation (Figure 1).
2
3.
Analytical reagent grade
acetonitrile was obtained from Labscan Ltd.
or Mallinckrodt Inc.
, and was used as received.
4.
An aqueous
4 × 10−4
M Na2·EDTA solution is prepared by dilution of
37.2
mg of ethylenediaminetetraacetic acid disodium salt hydrate
(Acros Chemical Company, Inc.) with deionized water
to the mark in a
250-mL volumetric flask.
5.
Oxone
®
(2KHSO5·KHSO4·K2SO4) was purchased from
Aldrich Chemical Company, Inc.
, and was used as received.
6.
Oxygen
is formed as by-product in two processes, the decomposition of
Oxone
®
by dioxiranes and self-decomposition of
Oxone
®
.
7.
The progress of the reaction is monitored by thin layer chromatography.
A 0.1-mL sample is removed and dissolved in
2 mL
of hexane
. The solution is spotted on a TLC plate
(1 cm × 4 cm, silica gel 60 F
254, Merck), and the plate is developed in
1:20 ethyl acetate/hexane
.Visualization
by short-wavelength ultraviolet light shows the olefin at R
f = 0.50 and
the epoxide at R
f = 0.35.
8.
Flash column chromatography
3
is performed on Merck silica gel 60 (230-400 mesh ASTM) with
5%
ethyl acetate in hexane
as eluent.
9.
trans-2-Methyl-2,3-diphenyloxirane
exhibits the following physical and spectroscopic characteristics:
mp 43.5-44.5°C; lit.
4
46-47°C;
1H NMR (500 MHz,
CDCl
3) δ: 1.47 (s, 3 H), 3.97 (s, 1 H),
7.28-7.48 (m, 10 H)
;
13C NMR (125 MHz, CDCl
3) δ: 16.9,
63.3, 67.3, 125.3, 126.7, 127.7,
127.9, 128.4, 128.7, 136.1, 142.5
;
EIMS (20 eV) m/z 210 (M
+,
91), 209 (52), 195 (44), 181 (39), 167
(100)
; HRMS for C
15H
14O
(M
+), calcd 210.1045, found 210.1047
.
Handling and Disposal of Hazardous Chemicals
The procedures in this article are intended for use only by persons with prior training in experimental organic chemistry. All hazardous materials should be handled using the standard procedures for work with chemicals described in references such as "Prudent Practices in the Laboratory" (The National Academies Press, Washington, D.C., 2011 www.nap.edu). All chemical waste should be disposed of in accordance with local regulations. For general guidelines for the management of chemical waste, see Chapter 8 of Prudent Practices.
These procedures must be conducted at one's own risk. Organic Syntheses, Inc., its Editors, and its Board of Directors do not warrant or guarantee the safety of individuals using these procedures and hereby disclaim any liability for any injuries or damages claimed to have resulted from or related in any way to the procedures herein.
3. Discussion
Dioxiranes
5 are powerful
oxidants for epoxidation of olefins under mild and neutral reaction conditions.
6
These epoxides are important and versatile intermediates in organic synthesis.
7 The most commonly used dioxiranes, i.e.,
dimethyldioxirane
and
methyl(trifluoromethyl)dioxirane
, can
be obtained by distillation.
8 For preparative epoxidation, an operationally simple
method is to generate dioxiranes in situ from ketones and
Oxone
®
.
Compared with
acetone
,
1,1,1-trifluoroacetone
is much more
reactive for in situ epoxidation although a 10-fold excess is usually used.
9 Therefore, it will be desirable to employ
commercially available ketones in low catalyst loading with a minimal amount of
Oxone
®
for epoxidation.
The procedure described here provides a simple and convenient method for the preparation
of a variety of epoxides. It uses
Oxone
®
,
an inexpensive, safe, and easily handled reagent as the terminal oxidant. The epoxidation
reactions are environmentally acceptable processes as
Oxone
®
only produces non-toxic
potassium hydrogen sulfate
and
oxygen
as the by-products.
As shown in the Table, with
5 mol% of 1,1-dioxotetrahydrothiopyran-4-one
as catalyst,
10
epoxidation of various olefins (2-mmol scale) in a homogeneous
acetonitrile-water
solvent system with
1.5 equiv of Oxone
®
at room temperature can be achieved in a short period of time with excellent yields
of epoxides (80-97%) isolated by flash column chromatography.
2
As the pH of the reaction is maintained at 7-7.5 by
sodium
bicarbonate
, acid- or base-labile epoxides (entries 12-14) can
be easily isolated without decomposition. More importantly, the in situ epoxidation
of olefins can be performed on a large scale directly with
5
mol% of tetrahydrothiopyran-4-one
, which is oxidized
immediately by
Oxone
®
to
1,1-dioxotetrahydrothiopyran-4-one
during the epoxidation reactions. For example, with
5 mol%
of tetrahydrothiopyran-4-one
, substrates
3,
5 (20 mmol each) and
11 (100 mmol) were epoxidized with excellent isolated
yields of epoxides (91-96%).
TABLE
IN SITU EPOXIDATION OF OLEFINS
|
|
Substrates:
|
|
|
| Entry |
Substrate |
Reaction Time (hr)a
|
Epoxide Yield (%)b
|
|
| 1 |
1
|
5 |
95 |
| 2 |
2
|
4.5 |
87 |
| 3 |
3
|
1.5 (1.7c) |
95 (96c) |
| 4 |
4
|
1.5 |
81 |
| 5 |
5
|
4 (3.5c) |
97 (91c) |
| 6 |
6
|
2.5 |
94 |
| 7 |
7
|
0.5 |
83 |
| 8 |
8
|
4 |
95 |
| 9 |
9
|
2.5 |
85 |
| 10 |
10
|
3 |
96 |
| 11 |
11
|
0.5 (2d) |
96 (92d) |
| 12 |
12
|
4.5 |
80 |
| 13 |
13
|
3.5 |
95 |
| 14 |
14
|
2.5 |
92 |
|
aTime for epoxidation to be completed
as shown by TLC or GC analysis.
|
|
|
c20-mmol scale reaction with 5 mol% of tetrahydrothiopyran-4-one
.
|
d100-mmol scale reaction with 5 mol% of tetrahydrothiopyran-4-one
.
|
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
Tetrahydrothiopyran-4-one:
4H-Thiopyran-4-one,
tetrahydro- (8,9); (1072-72-6)
Oxone:
Peroxymonosulfuric acid, monopotassium
salt, mixt. with
dipotassium sulfate and
potassium
hydrogen sulfate (9) (37222-66-5)
trans-2-Methyl-2,3-diphenyloxirane:
Oxirane,
2-methyl-2,3-diphenyl-, trans- (9); (23355-99-9)
trans-α-Methylstilbene:
Stilbene, α-methyl-,
(E)-;
Benzene, 1,1'-(1-methyl-1,2-ethenediyl)bis-, (E)-
(9); (833-81-8)
Acetonitrile (8,9); (75-05-8)
Ethylenediaminetetraacetic acid, disodium salt, dihydrate:
Acetic acid, (ethylenedinitrilo)tetra-, disodium salt, dihydrate
(8);
Glycine, N,N'-1,2-ethanediylbis[N-(carboxymethyl)-, disodium
salt, dihydrate (9); (6381-92-6)
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