trans-3-Penten-2-one

[3102-33-8]  · C5H8O  · trans-3-Penten-2-one  · (MW 84.13)

(undergoes conjugate addition as in Michael1-3 and cuprate4 reactions; reagent for Robinson annulation5-11 and Diels-Alder12 reaction)

Physical Data: bp 121.5-124 °C; d204 0.8624 g cm-3; n25D 1.4329.

Solubility: sol water and all organic solvents.

Form Supplied in: liquid; commercial material is often contaminated with 3-penten-2-ol which is difficult to remove by distillation.

Analysis of Reagent Purity: IR, NMR, and GC.13

Preparative Methods: an excellent method14 involves the Wittig reaction of Acetylmethylenetriphenylphosphorane and Acetaldehyde (2.5 mol equiv) in methylene chloride (reflux, 6 h, 76% yield). Another good method13 proceeds via the Aluminum Chloride catalyzed addition of Acetyl Chloride to propene followed by dehydrochlorination.

Purification: fractional distillation.13,14

Handling, Storage, and Precautions: best stored in refrigerator; moderately toxic;15 lachrymator. This reagent should only be handled in a fume hood.

Conjugate Addition Reactions.

Enolates of esters,1 amides,2 ketones (eq 1),1 and organocuprates4 participate in conjugate addition reactions with trans-3-penten-2-one.

Basic conditions can be avoided by using the Lewis acid-catalyzed Michael reaction of enol silyl ethers with the reagent (eq 2).3

Robinson Annulation.

An important application of trans-3-penten-2-one is in the Robinson annulation reaction,5-11 which has been widely used for the synthesis of natural products such as eremophilane sesquiterpenes.5-7 Annulations involving this enone have been involved as key steps (eqs 3 and 4) in the total synthesis of isonootkatone5 and calarene.6

The steric outcome of these reactions is very dependent on the reaction conditions.5-9 In eq 4 the use of benzene as solvent gave a 10:1 ratio of the trans- and cis-dimethyl products while formamide gave a 1:1 ratio. Likewise, reaction of 2-methylcyclohexanone and trans-3-penten-2-one using Sodium Hydride in dioxane gave the cis-dimethyl product (eq 5), but DMSO gave the trans product.8 However, other workers reexamined this work and observed somewhat different yields and stereoselectivities.9

A variation of the Robinson annulation involves the Lewis acid-catalyzed reaction of a silyl enol ether with the enone (eq 6).11


1. Oare, D. A.; Heathcock, C. H. JOC 1990, 55, 157.
2. Oare, D. A.; Henderson, M. A.; Sanner, M. A.; Heathcock, C. H. JOC 1990, 55, 132.
3. Sato, T.; Wakahara, Y.; Otera, J.; Nozaki, H. T 1991, 47, 9773.
4. Lipshutz, B. H.; Wilhelm, R. S.; Kozlowski, J. A. JOC 1984, 49, 3938.
5. Marshall, J. A.; Warne, Jr., T. M. JOC 1971, 36, 178.
6. Coates, R. M.; Shaw, J. E. JACS 1970, 92, 5657.
7. Takagi, Y.; Nakahara, Y.; Matsui, M. T 1978, 34, 517.
8. Scanio, C. J. V.; Starrett, R. M. JACS 1971, 93, 1539.
9. Kikuchi, M.; Yoshikoshi, A. BCJ 1981, 54, 3420.
10. Dauben, W. G.; Bunce, R. A. JOC 1983, 48, 4642.
11. Huffman, J. W.; Potnis, S. M.; Satish, A. V. JOC 1985, 50, 4266.
12. Kelly, T. R.; Meghani, P.; Ekkundi, V. S. TL 1990, 31, 3381.
13. Odom, H. C.; Pinder, A. R. OS 1971, 51, 115; OSC 1988, 6, 883.
14. House, H. O.; Respess, W. L.; Whitesides, G. M. JOC 1966, 31, 3128.
15. Sax, N. I. Dangerous Properties of Industrial Materials, 5th ed.; Van Nostrand-Reinhold: New York, 1979; p 891.

James E. Shaw

Phillips Petroleum, Bartlesville, OK, USA



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