Org. Synth. 1978, 58, 43
DOI: 10.15227/orgsyn.058.0043
CATALYTIC OSMIUM TETROXIDE OXIDATION OF OLEFINS: cis-1,2-CYCLOHEXANEDIOL
Submitted by V. VanRheenen, D. Y. Cha, and W. M. Hartley
1.
Checked by N. Meyer, W. Wykypiel, and D. Seebach.
1. Procedure
Caution! Care should be taken in handling osmium tetroxide. The vapor is toxic, causing damage to eyes, respiratory tract, and skin.
A. N-Methylmorpholine N-oxide (1) (Note 1). A 100-ml., three-necked, round-bottomed flask equipped with a reflux condenser, a magnetic stirring bar, and a dropping funnel is flushed with nitrogen or argon and charged with 32.3 g. (35.1 ml., 0.320 mole) of N-methylmorpholine (Note 2). The flask is immersed in an oil bath maintained at 75°, and 32.4 g. (29.1 ml., 0.286 mole) of 30% aqueous hydrogen peroxide is added dropwise over a period of 2.5 hours (Note 3). The mixture is stirred for 20 hours at 75°, at which time a negative peroxide test (potassium iodide paper) is obtained (Note 4). The reaction mixture is cooled to 50°, and a slurry of 50 ml. of methanol, 0.5 g. of charcoal, and 0.5 g. of Celite (Note 5) is added. After being stirred for 1 hour, the mixture is filtered and the filter cake washed with three 15-ml. portions of methanol. The filtrate and combined washings are concentrated with a rotary evaporator (water aspirator vacuum), with the bath temperature finally reaching 95°, where it is held for 10 minutes. The flask is fitted with a reflux condenser, and the residual viscous oil is dissolved in 25 ml. of acetone at 60°. On cooling to 40° (with seeding, if crystals of the N-oxide are available) the product spontaneously crystallizes. The slurry is stored at room temperature overnight, cooled in an ice bath, and filtered. The crystals are washed with three 15-ml. portions of 0° acetone and dried overnight at 40° (0.01 mm.) The yield of colorless crystalline monohydrate 1 is 32.4–34.3 g. (83.8–88.7%), m.p. 75–76° (Note 6) and (Note 7).
B.
cis-1,2-Cyclohexanediol (2). A
250-ml., three-necked, round-bottomed flask, with a
magnetic stirrer and a
nitrogen inlet, is charged with
14.81 g. (0.1097 mole) of monohydrate 1, 40 ml. of water, and
20 ml. of acetone. To this solution is added
ca. 70 mg. of osmium tetroxide (0.27 mmole) (Note 8) and
8.19 g. (10.1 ml., 0.100 mole) of cyclohexene (Note 9). This two-phase solution is stirred vigorously under
nitrogen at room temperature. The reaction is slightly exothermic and is maintained at room temperature with a
water bath. During the overnight stirring period, the reaction mixture becomes homogeneous and light brown in color. After 18 hours, TLC
(Note 10) shows the reaction to be complete.
Sodium hydrosulfite (0.5 g.) (Note 11) and
5 g. of Magnesol (Note 12) slurried in 20 ml. of water are added, the slurry is stirred for 10 minutes, and the mixture is filtered through a pad of
5 g. of Celite on a
150-ml. sintered-glass funnel. The Celite cake is washed with three
15-ml. portions of acetone. The filtrate, combined with
acetone wash, is neutralized to pH 7 with
6.4 ml. of 12 N sulfuric acid. The
acetone is evaporated under vacuum using a rotary evaporator. The pH of the resulting aqueous solution is adjusted to pH 2 with
2.3 ml. of 12 N sulfuric acid, and the
cis-diol
2 is separated from
N-methylmorpholine hydrosulfate by extraction with five
45-ml. portions of n-butanol (Note 13). The combined
butanol extracts are extracted once with
25 ml. of 25% sodium chloride solution, and the aqueous phase is backwashed with
50 ml. of butanol. The
butanol extracts are evaporated under vacuum, giving
12.1 g. of white solid. The
cis-diol
2 is separated from a small amount of insoluble material (
ca. 0.7 g.) by boiling the solid with a
200-ml., an 80-ml., and a 20-ml. portion of diisopropyl ether (Note 14), decanting the solvent each time. The combined ether fractions are evaporated to
ca. 50 ml. under vacuum, and crystalline white plates precipitate. The mixture is cooled to
ca. −15°. The crystals are filtered, washed with two
10-ml. portions of cold diisopropyl ether, and dried, yielding
10.18–10.32 g. (
89–90%) of the
cis-diol
2 (m.p.
96–97°).
2. Notes
1.
N-Methylmorpholine N-oxide (1) can also be purchased from Eastman Organic Chemicals or Fluka A G.
2.
Commercial material was used without purification (the purity was checked by refractive index and
1H NMR).
3.
The slow addition (2.5 hours) is required to avoid overheating of the reaction mixture. The potential danger of using
hydrogen peroxide at an elevated temperature is minimized by using a 10% excess of
N-methylmorpholine and by choosing reaction conditions that ensure rapid consumption, avoiding accumulation of peroxide in the mixture. A
50% aqueous hydrogen peroxide solution can also be used. The content of the commercial
hydrogen peroxide (ca. 30 or 50%) must be determined by iodometric titration.
4.
Very sensitive ether peroxide test strips (Merckoquant, Art. No. 10011), available from E. Merck, Darmstadt, are used. If the test is still positive at this point, an additional
0.2 ml. of N-methylmorpholine is added. Stirring and heating at 75° are continued for another 5 hours. Remaining peroxide renders the work-up and drying of the product potentially hazardous.
N-Methylmorpholine N-oxide (
1) and
hydrogen peroxide form a strong 1:1 complex. In the reaction with
osmium tetroxide, this complex produces conditions similar to those of the Milas reaction,
2 and some ketol formation may result.
5.
Darco G 60, Aktivkohle, Fluka A G No. 05100, and Celite 512 Hyflosuper, Firma Schneider, Winterthur, Switzerland, No. 5100025, were used.
6.
The procedure is designed to maintain the proper amount of water in the crystallization mixture so that the monohydrate
1 is obtained. It has the highest melting point and is the least hydroscopic. Other hydrated forms, such as the dihydrate (m.p. 35–60°) and mixed hydrates, may be isolated. A Karl Fischer assay of the water content is not necessary if the obtained material melts within the range given.
7.
A second crop of
1.7–4.3 g. (
4.3–11.1%) of the product can be obtained by evaporating the mother liquid, heating the residue at 97° for 20 minutes under reduced pressure, dissolving it in
55 ml. of acetone at 60°, and continuing as described.
8.
Commercial
osmium tetroxide was used without purification. It is not easy to accurately weigh this material because it rapidly sublimes.
9.
Commercial
cyclohexene was used (the purity was checked by refractive index). Addition of
cyclohexene caused a darkening of the reaction mixture. This is caused by a finite concentration of the osmate ester. The reaction becomes lighter in color when complete.
10.
The reaction may be followed by TLC. The ratio of the
Rf values for
cyclohexene and
cis-diol
2 is 2:1 (commercial silica gel plates,
ethyl acetate). The plates are best visualized by first spraying with
1% aqueous potassium permanganate, then with methanolic
sulfuric acid, followed by charring with heat. The checkers found that, if the procedure is followed exactly, monitoring the reaction by TLC is unnecessary.
11.
Sodium hydrosulfite reduces the
osmium tetroxide to insoluble lower-valent
osmium species.
12.
The submitter used
Magnesol, industrial grade, available from Reagent Chemical Research, Inc., Pilot Engineering Division. The checkers used Florisil TLC, available from E. Merck, Darmstadt, No. 12519.
13.
Since the
cis-diol
2 is very water soluble, a polar solvent such as
n-butanol is required to extract it.
n-Butanol forms an efficient water azeotrope. More conventional solvents may be used for less polar products.
14.
Diisopropyl ether readily forms explosive peroxides. It should be tested for peroxides, and contact with air should be minimized.
3. Discussion
cis-Dihydroxylation of olefins may be effected with
potassium permanganate,
osmium tetroxide, or
silver iodoacetate according to Woodward's procedure.
3 Oxidation of
cyclohexene to
cis-diol
2 with
potassium permanganate is reported to proceed in only
30–40% yields.
4,5 A modification of Woodward's procedure, in which
iodine,
potassium iodate, and
potassium acetate in
acetic acid were used, has given
cis-diol
2 in 86% yield.
6 This procedure is particularly useful for placement of
cis-diols on the more hindered side of more complex substrates.
The reaction of an olefin with
osmium tetroxide is the most reliable method for
cis-dihydroxylation of a double bond, particularly for preparation of
cis-diols on the least hindered side of the molecule. When used stoichiometrically, however, the high cost of
osmium tetroxide can make a large-scale glycolization prohibitively expensive, and the work-up procedures can be cumbersome, particularly when
pyridine is used. Also
osmium tetroxide is volatile and toxic, resulting in handling problems. Catalytic osmylation using chlorate
7 or
hydrogen peroxide (Milas reagent
2) to regenerate
osmium tetroxide avoids some of these problems, but overoxidation to an α-ketol commonly leads to losses in yield and separation problems. Preparation of
cis-diol
2 with
sodium chlorate and
osmium tetroxide is reported to proceed in
46% yield,
4 and in
76% yield
8 when
sodium chlorate,
potassium osmate, and a detergent are used. A
62% yield of the
cis-diol
2 from
cyclohexene is reported in an interesting catalytic osmylation using
tert-butyl hydroperoxide under alkaline conditions.
9 This method is particularly useful for oxidation of tri- and tetrasubstituted olefins.
In this report we describe the conversion of cyclohexene to cis-diol 2, in 90% yield, by catalytic osmylation using 1 mole equivalent of N-methylmorpholine N-oxide (1, NMO) to regenerate the osmium tetroxide catalyst. This procedure avoids the α-ketol by-products encountered with the currently available catalytic processes, and provides the high yields of the stoichiometric reaction without the expense and work-up problems.
The reaction is generally applicable to a variety of substrate types, as illustrated in Table I.
10 Compatible functionality includes hydroxyl, ester, lactone, acid, ketone, and electron-poor olefins such as those conjugated to α-ketones. Some selectivity between isolated double bonds is also found. The reaction generally gives nearly quantitative yields with simple olefins.
TABLE I
PREPARATION OF cis-DIOLS BY CATALYTIC OXIDATION OF OLEFINS WITH OSMIUM TETROXIDE
|
|
Starting Material
|
Product
|
|
Procedure
|
(Isolated yields, %)
|
Reference
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| |
|
|
|
NMOa-OsO4
|
(79)
|
10b
|
|
NaClO3-OsO4
|
(30)
|
12
|
|
KMnO4
|
(50)
|
13
|
|
H2O2-OsO4
|
(11.4)
|
12
|
| |
|
|
|
|
| |
|
|
|
NMOa-OsO4
|
(31)
|
10b
|
|
OsO4, 1 mole
|
(14)
|
14
|
|
KMnO4
|
(3)
|
15
|
| |
|
|
|
|
| |
|
|
|
NMOa-OsO4
|
(25)
|
10b
|
|
OsO4, 1 mole
|
(21)
|
16
|
|
KMnO4
|
(28)
|
16
|
| |
|
|
|
|
| |
|
|
|
NMOa-OsO4
|
(55)
|
10b
|
|
OsO4, 1 mole
|
(53)
|
17
|
|
KClO3-OsO4
|
(35)
|
17
|
| |
|
|
|
|
| |
|
|
|
NMOa-OsO4
|
(78)
|
18c
|
|
NaClO3-OsO4
|
(79)
|
18c
|
| |
|
|
aNMO = N-Methylmorpholine N-oxide.
|
bThe reaction was carried out in aqueous acetone at room temperature using 0.2–1.0 mole % OsO4 (see Experimental section).
|
cSolvent composition of 10:3:1 tert-butanol–tetrahydrofuran–water was preferred for this reaction.
|
The reaction is usually run in aqueous acetone in either one- or two-phase systems, but substrate solubility may require the use of other solvents. Aqueous tert-butanol, tetrahydrofuran, and the mixtures of these solvents have also been used successfully.
Other simple aliphatic amine oxides can be used as the oxidant in this reaction, but N-methylmorpholine N-oxide (1) is preferred because it generally gives a faster reaction rate and is easily prepared. The reaction can also be used to convert aliphatic amine oxides into amines.
This preparation is referenced from:
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
potassium osmate
sulfuric acid (7664-93-9)
acetic acid (64-19-7)
ethyl acetate (141-78-6)
methanol (67-56-1)
potassium permanganate (7722-64-7)
Cyclohexene (110-83-8)
sodium chloride (7647-14-5)
nitrogen (7727-37-9)
sodium hydrosulfite (7775-14-6)
butanol,
n-butanol (71-36-3)
iodine (7553-56-2)
acetone (67-64-1)
pyridine (110-86-1)
sodium chlorate (7775-09-9)
hydrogen peroxide (7722-84-1)
potassium acetate (127-08-2)
Tetrahydrofuran (109-99-9)
diisopropyl ether (108-20-3)
osmium tetroxide (20816-12-0)
argon (7440-37-1)
tert-butanol (75-65-0)
Magnesol
osmium
silver iodoacetate
potassium iodate (7758-05-6)
tert-butyl hydroperoxide (75-91-2)
N-methylmorpholine N-oxide (80913-66-2)
N-methylmorpholine (109-02-4)
cis-1,2-Cyclohexanediol (1792-81-0)
N-methylmorpholine hydrosulfate
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