[504-60-9]  · C5H8  · 1,3-Pentadiene  · (MW 68.13) (cis)

[1574-41-0] (trans)


(widely used diene for Diels-Alder cycloaddition reactions;1 common ligand in transition metal-pentadienyl complexes2)

Alternate Name: piperylene.

Physical Data: cis: mp -141 °C; bp 44 °C; d 0.691 g cm-3. trans: mp -87.5 °C; bp 42 °C; d 0.683 g cm-3. Mixture of isomers: bp 42 °C; d 0.683 g cm-3.

Solubility: sol alcohol, acetone, ether, benzene, heptane; insol H2O.

Form Supplied in: widely available as cis isomer, trans isomer, and as a mixture of isomers.

Purification: colorless liquid distilled from NaBH4; purified by preparative gas chromatography.

Handling, Storage, and Precautions: flammable liquid, irritant.

Diels-Alder Reactions.1

The trans isomer of piperylene has been widely used in cycloaddition reactions to construct six-membered carbocyclic3-10 and heterocyclic rings.11-15 The electron-donating ability of the methyl group causes trans-piperylene to be 3-5 times more reactive than 1,3-Butadiene in Diels-Alder reactions with Maleic Anhydride or Tetracyanoethylene (TCNE).3c,4 Unlike trans-piperylene, the cis isomer is known to be very unreactive except with highly activated dienophiles, and generally undergoes polymerization reactions (eq 1).3 In reaction with TCNE, cis-piperylene has been estimated to be over 105 less reactive than the trans isomer.3c The unfavorable steric interactions between the methyl group and the vinyl hydrogens in the s-cis conformation of cis-piperylene, required in the transition state for the Diels-Alder, are thought to be responsible for the lower reactivity.1 Both piperylenes give predominently the endo Diels-Alder products.

As with other unsymmetrical dienes, the Diels-Alder reactions of piperylene obey the ortho rule,1 which predicts that the electron-donating group will be adjacent (ortho) to the electron-withdrawing substituent on the dienophile (eq 2).5 Similar selectivities are observed for Acrylonitrile and Acrolein.1,3 In general, the regio- and endoselectivities are higher at lower reaction temperatures and, especially, in the presence of Lewis acids such as Aluminum Chloride.6

The reactions with more complex dienophiles have shown similar regio- and endoselectivities.6 The cycloadditions between trans-1,3-pentadiene and substituted quinones give products with high endoselectivity and with expected regiochemistry based on electronic considerations (eqs 3 and 4).7,8 A remarkable reversal in regioselectivity was achieved for 2,6-dimethylbenzoquinone by using a Lewis acid for the reaction (eq 4).8 In the cycloadditions with a substituted 2,5-cyclohexadienone, exclusive addition from the ester face was observed (eq 5).9 Other examples showing endo-, regio-, and facial selectivity are known (eq 6).10,6

The use of 1,3-pentadiene in hetero-Diels-Alder reactions is well precedented.11 It reacts with carbonyls,12 imines,13 nitroso groups,14 and other heterodienophiles15 to yield the corresponding heterocycles. For example, the in situ generated sulfonyl imine from propanal can be effectively trapped by 1,3-pentadiene in a [4 + 2] cycloaddition reaction (eq 7).13a

More recently, 1,3-pentadiene has been used in asymmetric Diels-Alder reactions, yielding carbocycloadditions16 and heterocycloadditions.13 The asymmetry can be induced by a chiral auxiliary on the dienophile (eq 8)16a or by a chiral Lewis acid (eq 9).17

The rhodium(II)-catalyzed decomposition of vinyldiazomethanes in the presence of cis- and trans-1,3-pentadienes generates cycloheptadienes with complete stereocontrol (eq 10).18

Complexes with Transition Metals.

Many transition metal complexes of 1,3-pentadiene, which coordinates as the pentadienyl ligand, are known. The complexes are generally h5 (e.g. 3, 4) or h3 (e.g. 5-8).2 Both modes of coordination are found in compound (9).19

While the first complex of a pentadienyl ligand, Fe(C5H7)(CO)3, was prepared in 1962 by protonation of the neutral Fe(h4-pentadienyl)(CO)3,20 until recently there was little indication that pentadienyl complexes might lead to potentially useful carbon-carbon bond-forming reactions. Recent reports have described the addition of nucleophiles to neutral (h5-pentadienyl)maganese,21 -iron, or -ruthenium19 complexes to generate novel (s,h3-pentadienyl) complexes (eq 11).21 Under photochemical conditions, the tricarbonyl(h5-pentadienyl)manganese complex reacts with conjugated dienes, such as trans- or cis-piperylenes, in a formal [4 + 5] cycloaddition to give macrocyclic complexes (eq 12).22

1. (a) Martin, J. G.; Hill, R. K. CRV 1961, 61, 537. (b) Titov, Y. A. RCR 1962, 31, 267. (c) Guseinov, I. I.; Vasilev, G. S. RCR 1963, 32, 20. (d) Sauer, J. AG(E) 1966, 5, 211. (e) Sauer, J. AG(E) 1967, 6, 16. (f) Oppolzer, W. COS 1991, 5, 315.
2. Ernst, R. D. CRV 1988, 88, 1255.
3. (a) Frank, R. L.; Emmick, R. D.; Johnson, R. S. JACS 1947, 69, 2313. (b) Craig, D. JACS 1950, 72, 1678. (c) Stewart, C. A. JOC 1963, 28, 3320. (d) Brocksom, T. J.; Constantino, M. G. JOC 1982, 47, 3450. (e) Vijn, R. J.; Hiemstra, H.; Kok, J. J.; Knotter, M.; Speckamp, W. N. T 1987, 43, 5019. (f) Okada, K.; Kondo, M.; Tanino, H.; Kakoi, H.; Inoue, S. H 1992, 34, 589.
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5. Inukai, T.; Kojima, T. JOC 1967, 32, 869.
6. (a) Ayyar, K. S.; Cookson, R. C.; Kagi, D. A. CC 1973, 161. (b) Corey, E. J.; Estreicher, H. TL 1981, 22, 603. (c) Knapp, S.; Lis, R.; Michna, P. JOC 1981, 46, 624. (d) Hendrickson, J. B.; Singh, V. CC 1983, 837. (e) Fringueli, F.; Pizzo, F.; Taticchi, A.; Wenkert, E. JOC 1983, 48, 2802. (f) Weller, D. D.; Stirchak, E. P. JOC 1983, 48, 4873. (g) Angell, E. C.; Fringueli, F.; Pizzo, F.; Porter, B.; Taticchi, A.; Wenkert, E. JOC 1985, 50, 4696. (h) Ono, N.; Miyake, H.; Kamimura, A.; Kaji, A. JCS(P1) 1987, 1929. (i) Ono, N.; Kamimura, A.; Kaji, A. JOC 1988, 53, 251. (j) Singleton, D. A.; Martinez, J. P. JACS 1990, 112, 7423. (k) Alunni, S.; Minuti, L.; Pasciuti, P.; Taticchi, A.; Guo, M.; Wenkert, E. JOC 1991, 56, 5353. (l) Minuti, L.; Selvaggi, R.; Taticchi, A.; Guo, M.; Wenkert, E. CJC 1992, 70, 1481. (m) Okada, K.; Mizuno, Y.; Tanino, H.; Kakoi, H.; Inoue, S. CPB 1992, 40, 1110. (n) Bruce, J. M.; Lloyd-Williams, P. JCS(P1) 1992, 2877. (o) Singleton, D. A.; Martinez, J. P.; Watson, J. V.; Ndip, G. M. T 1992, 48, 5831. (p) Wenkert, E.; Vial, C.; Näf, F. C 1992, 46, 95. (q) Minuti, L.; Selvaggi, R.; Taticchi, A.; Sandor, P. T 1993, 49, 1071.
7. Bohlmann, F.; Förster, H. J.; Fischer, C. H. LA 1976, 1487.
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11. Weinreb, S. M.; Staib, R. R. T 1982, 38, 3087.
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Hua M. Zhong & Viresh H. Rawal

The Ohio State University, Columbus, OH, USA

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