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Org. Synth. 1967, 47, 87
DOI: 10.15227/orgsyn.047.0087
5-METHYL-5-HEXEN-2-ONE
[5-Methylene-2-hexanone]
Submitted by Sandra Boatman and Charles R. Hauser1.
Checked by E. J. Corey and William E. Russey.
1. Procedure
In a 1-l. round-bottomed flask equipped with a condenser are placed 78.0 g. (0.56 mole) of commercial anhydrous potassium carbonate, 45.0 g. (0.50 mole) of methallyl chloride (Note 1), 55.0 g. (0.55 mole) of 2,4-pentanedione (Note 1), and 300 ml. of anhydrous ethanol (Note 2). The mixture is refluxed on a steam bath for 16 hours. The condenser is replaced by a distilling head and condenser, and about 200 ml. of ethanol is distilled from the mixture (Note 3). Ice water (600 ml.) is added to dissolve the salts, and the mixture is extracted three times with ether. The combined ether extracts are washed twice with 100 ml. of saturated sodium chloride solution, dried for 30 minutes over anhydrous magnesium sulfate, and filtered; the solvent is evaporated. The residue is distilled through a 6-in. Vigreux column using an oil bath maintained at 190° to give 26–29 g. (47–52%) of the product, b.p. 145–155° (Note 4), (Note 5).
2. Notes
1. Eastman Organic Chemicals practical grade methallyl chloride was distilled (b.p. 70–71°); Union Carbide Chemicals Co. 2,4-pentanedione was distilled (b.p. 134.5–135.5°).
2. Commercial grade absolute ethanol was dried over Linde 3A molecular sieves.
3. At this point most of the ethyl acetate, which is formed as a by-product of the reaction, also is removed.
4. The checkers used a 2-ft. spinning-band column at 200 mm. and observed b.p. 110–111.5°.
5. In the distillation residue (5.7–6.3 g.) remain other byproducts, presumably 1,1-dimethallyl-2-propanone, 3-methallyl-2,4-pentanedione, and 3,3-dimethallyl-2,4-pentanedione (indicated by vapor phase chromatography). The checkers carried out v.p.c. analyses using an 8-ft. column of 5% silicone oil XE-60 on Diatoport S at 100° for analysis of the distillate and 175° for analysis of the residue.
3. Discussion
5-Methyl-5-hexen-2-one has been prepared by alkylation of acetoacetic ester with methallyl chloride, followed by cleavage; the overall yield in the two steps was 51%.2
4. Merits of the Preparation
The present procedure, which is characterized by its extreme simplicity, has been employed to prepare various ketones of type RCH2COCH3 from 2,4-pentanedione,3 as indicated in Table I.
This preparation is referenced from:
TABLE I ALKYLATION AND CLEAVAGE OF 2,4-PENTANEDIONE

Alkyl Halide

Ketone

% Yield


Benzyl chloride

4-Phenyl-2-butanone

73

o-Bromobenzyl bromide

4-(o-Bromophenyl)-2-butanone

75

m-Bromobenzyl bromide

4-(m-Bromophenyl)-2-butanone

78

o-Chlorobenzyl chloride

4-(o-Chlorophenyl)-2-butanone

78

m-Chlorobenzyl bromide

4-(m-Chlorophenyl)-2-butanone

65

p-Chlorobenzyl bromide

4-(p-Chlorophenyl)-2-butanone

62

m-Fluorobenzyl chloride

4-(m-Fluorophenyl)-2-butanone

60

m-Nitrobenzyl chloride

4-(m-Nitrophenyl)-2-butanone

65

α-Chloromethylnaphthalen

4-(α-Naphthyl)-2-butanone

61

Phenacyl chloride

1-Phenyl-1,4-pentanedione

55

n-Butyl iodide

2-Heptanone

60



References and Notes
  1. Department of Chemistry, Duke University, Durham, North Carolina. This work was supported by the National Science Foundation.
  2. W. Kimel and A. C. Cope, J. Am. Chem. Soc., 65, 1992 (1943).
  3. S. Boatman, T. M. Harris, and C. R. Hauser, J. Org. Chem., 30, 3321 (1965).

Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

ethanol (64-17-5)

potassium carbonate (584-08-7)

ethyl acetate (141-78-6)

ether (60-29-7)

sodium chloride (7647-14-5)

benzyl chloride (100-44-7)

2-Heptanone (110-43-0)

magnesium sulfate (7487-88-9)

2,4-pentanedione (123-54-6)

phenacyl chloride (532-27-4)

α-Chloromethylnaphthalen (86-52-2)

methallyl chloride (563-47-3)

o-Chlorobenzyl chloride (611-19-8)

5-Methyl-5-hexen-2-one,
5-Methylene-2-hexanone (3240-09-3)

3,3-dimethallyl-2,4-pentanedione

4-Phenyl-2-butanone (2550-26-7)

4-(α-Naphthyl)-2-butanone

1-Phenyl-1,4-pentanedione (583-05-1)

4-(p-Chlorophenyl)-2-butanone (3506-75-0)

n-Butyl iodide (542-69-8)

p-chlorobenzyl bromide (622-95-7)

o-Bromobenzyl bromide (3433-80-5)

4-(o-Bromophenyl)-2-butanone

m-Bromobenzyl bromide (823-78-9)

4-(m-Bromophenyl)-2-butanone

4-(o-Chlorophenyl)-2-butanone

m-Chlorobenzyl bromide (766-80-3)

4-(m-Chlorophenyl)-2-butanone

m-Fluorobenzyl chloride (456-42-8)

4-(m-Fluorophenyl)-2-butanone

m-Nitrobenzyl chloride (619-23-8)

4-(m-Nitrophenyl)-2-butanone

1,1-dimethallyl-2-propanone

3-methallyl-2,4-pentanedione