Organic Syntheses, CV 6, 462
Submitted by M. Nakagawa
1, J. Saegusa
1, M. Tonozuka
1, M. Obi
1, M. Kiuchi
1, T. Hino
1, and Y. Ban
2.
Checked by A. Wick, D. Ehrlich, and A. Brossi.
1. Procedure
A.
5,6-Dihydro-2H-pyran-2-one. In a
500-ml., one-necked, round-bottomed flask equipped with a
reflux condenser are combined
43 g. (0.50 mole) of vinylacetic acid (Note
1),
30 g. (1 mole as CH2O) of paraformaldehyde (Note
2),
3 ml. of concentrated sulfuric acid, and
125 ml. of glacial acetic acid. This mixture is refluxed gently for 3 hours, then cooled to room temperature and swirled while
16 g. of anhydrous sodium acetate is added.
Acetic acid is removed at 50–55° on a
rotary evaporator, 100 ml. of water is added, and the flask is fitted with a
two-necked adapter, a
thermometer, and a
magnetic stirring bar. The flask is then immersed in an
ice bath, and the solution is brought to pH 8 with aqueous
20% sodium hydroxide (Note
3), which is added dropwise and with stirring at a rate such that the temperature remains below 5°. The resulting solution is transferred to a
1-l. separatory funnel and extracted with four
300-ml. portions of dichloromethane (Note
4). After being washed with one
150-ml. portion of saturated aqueous sodium chloride (Note
5), the combined organic extracts are dried over anhydrous
sodium sulfate and filtered. Removal of
dichloromethane with a rotary evaporator leaves a mobile yellow oil, which is distilled under reduced pressure, yielding
12.3 g. (
25.1%) of
5,6-dihydro-2H-pyran-2-one, b.p.
114–117° (18–19 mm.) (Note
6).
B.
2H-Pyran-2-one. A mixture of
9.81 g. (0.100 mole) of 5,6-dihydro-2H-pyran-2-one,
200 mg. of benzoyl peroxide,
18.6 g. (0.105 mole) of N-bromosuccinimide (Note
7), and
800 ml. of carbon tetrachloride is prepared in a
2-l., three-necked, round-bottomed flask equipped with a reflux condenser and a
mechanical stirrer. The resulting suspension is stirred and heated to reflux. After 1.5 hours at reflux, most of the solid is dissolved, and the solution gives a negative test with starch–iodide paper. The reaction mixture is then allowed to cool, during which time
succinimide crystallizes out. The precipitate is removed by filtration, and the filtrate is concentrated under reduced pressure, leaving crude
5-bromo-5,6-dihydro-2H-pyran-2-one as an oil.
This residue is stirred at room temperature while
150 ml. of triethylamine (Note
8) is added.
Triethylamine hydrobromide begins to precipitate soon after the addition is started, and the resulting slurry is refluxed gently for 15 minutes. It is then cooled to room temperature, and the insoluble material is removed by filtration and washed with
benzene. Concentration of the combined filtrates under reduced pressure leaves an oily residue, which is dissolved in
600 ml. of diethyl ether. The ethereal solution is transferred to a 1-l. separatory funnel, washed with two
20-ml. portions of saturated aqueous sodium chloride, dried over anhydrous
sodium sulfate, and filtered.
Ether is removed with a rotary evaporator, and the resulting oil is distilled at reduced pressure. A forerun of
265 mg. is collected below
103° (22 mm.) before
6.7 g. (
70%) of
2H-pyran-2-one distils as a colorless oil, b.p.
103–111° (19–22 mm.) (Note
9).
2. Notes
1.
Vinylacetic acid is available from Tokyokasei Company, Ltd., Japan or from Fluka AG, Buchs, Switzerland. Commercial material, which shows about 3% of
crotonic acid in its
1H NMR spectrum, was distilled at 90–92° (40–43 mm.) prior to use.
2. The submitters obtained
paraformaldehyde from Koso Chemical Company, Inc., Japan.
3. About 180 ml. is required.
4. In these extractions, the organic layer is the lower one. If the two phases do not separate readily, fine-grained precipitates are probably at fault. These may be removed by filtration through a
Büchner funnel.
6. A forerun of approximately
180 mg. is collected below
110° (18 mm.). The IR spectrum of this material is practically identical with that of the main distillate. Reported physical constants for
5,6-dihydro-2H-pyran-2-one are: b.p.
110° (15 mm.) and
n25D 1.4730.
3
7. The submitters obtained
N-bromosuccinimide from Nakarai Chemicals Ltd., Japan, and crystallized it from water prior to use (m.p.
168–175°).
9. The IR spectrum of this material was essentially identical to that of the redistillate, b.p.
115–118° (37 mm.). Reported physical constants for
2H-pyran-2-one are: b.p.
206–209° (atmospheric pressure),
n25D 1.5272,
4 and b.p.
110° (26 mm.),
n25D 1.5270.
5
3. Discussion
The present one-step procedure for preparation of
5,6-dihydro-2H-pyran-2-one is slightly modified from that described in the original paper.
9 It is simpler and easier than the three-step method
3 used in the past and represents the most convenient synthesis currently available. The present preparation of
2H-pyran-2-one has several advantages compared to the alternatives mentioned above: simplicity of apparatus and technique, mild reaction conditions, availability of reactants, and ease of product isolation.
This preparation is referenced from:
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