Organic Syntheses Procedure

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Org. Synth. 1989, 67, 202

DOI: 10.15227/orgsyn.067.0202

4-METHOXY-3-PENTEN-2-ONE

[3-Penten-2-one, 4-methoxy-]

Submitted by George A. Kraus, Michael E. Krolski, and James Sy¹.

Checked by Yun Gao and K. Barry Sharpless.

1. Procedure

4-Methoxy-3-penten-2-one. A flame-dried, 250-mL, one-necked flask equipped with a condenser and a drying tube is charged with 2,4-pentanedione (Note 1) (25.0 g, 250 mmol), trimethyl orthoformate (Note 2) (26.53 g, 250 mmol), p-toluenesulfonic acid (0.54 g. 2.8 mmol), and methanol (Note 3) (62 mL). The flask is placed in an oil bath and heated at 55°C for 5 hr. The solution is cooled and concentrated under reduced pressure. Then 50 mL of CCl₄ is added and the solution is again concentrated under reduced pressure. The crude product is distilled via a short-path condenser and collected in a flask cooled in an ice bath (Note 4). The product distills at 43–47°C (4 mm) at an oil-bath temperature of 60°C (Note 5). The yield of pure product is 17.3–18.8 g (61–66%) (Note 6).

2. Notes

1. 2,4-Pentanedione was obtained from Aldrich Chemical Company, Inc. Its purity was greater than 99% and was used without purification.

2. The trimethyl orthoformate used in this experiment was obtained from Aldrich Chemical Company, Inc. Its purity was listed as 98% and was used without purification.

3. Methanol was obtained from Fisher Scientific. It was anhydrous-grade methanol.

4. The checkers used a dry ice–acetone cooling bath.

5. Use of higher temperature (>65°C) results in a much lower yield.

6. The spectral properties of 4-methoxy-3-penten-1-one are as follows: IR (neat) cm⁻¹: 1674, 1590, 1165, 922. NMR (CDCl₃) δ: 2.15 (s, 3 H), 2.28 (s, 3 H), 3.64 (s, 3 H), 5.41 (s, 1 H).

3. Discussion

4-Methoxy-3-penten-2-one has been prepared by Awang using methanol and sulfuric acid.² He also determined the stereochemistry by NMR solvent shift data and observation of nuclear Overhauser effects. Our preparation is a convenient, one-pot procedure. The title compound is useful for effecting the overall γ-alkylation of enones³ and has been used in a synthesis of prostaglandins.⁴

References and Notes

Department of Chemistry, Iowa State University, Ames, IA 50011.
Awang, D. V. C. Can. J. Chem. 1971, 49, 2672.
Stork, G.; Kraus, G. A. J. Am. Chem. Soc. 1976, 98, 2351.
Stork, G.; Kraus, G. A. J. Am. Chem. Soc. 1976, 98, 6747.

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

sulfuric acid (7664-93-9)

methanol (67-56-1)

CCl₄ (56-23-5)

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

p-toluenesulfonic acid (104-15-4)

trimethyl orthoformate (149-73-5)

4-Methoxy-3-penten-2-one,
3-Penten-2-one, 4-methoxy- (2845-83-2)

4-methoxy-3-penten-1-one

Notes

References/EndNotes

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