[15935-94-1]  · C21H19P  · Allylidenetriphenylphosphorane  · (MW 302.36)

(Wittig reagent for 1,3-diene synthesis2 and Michael addition reaction3)

Physical Data: 13C and 31P NMR solution studies,4 X-ray structures of the molybdenum and tungsten complexes,5 and the heat of formation (DH) have been reported.6

Solubility: sol THF,7 toluene.8

Form Supplied in: prepared in situ and used directly.

Preparative Methods: this Wittig reagent is generally prepared from Allyltriphenylphosphonium Bromide or chloride by treatment with n-Butyllithium or Phenyllithium.2,3,9 Structurally related analogs have been prepared by the similar methods: 2-butenylidenetriphenylphosphorane;10 3-methyl-2-butenylidenetriphenylphosphorane;10 (E)-2-octenylidenetriphenylphosphorane;11 (E)-pentadienylidenetriphenylphosphorane;11 (E)-2,4-hexadienylidenetriphenylphosphorane;12 2-alkynylidenetriphenylphosphorane;12 allylidenetributylphosphorane.13 g-Alkyl-substituted allylidenetriphenylphosphorane can be also obtained by the reaction of diisobutylaluminum alkylideneamide with methylidenetriphenylphosphorane.14

Handling, Storage, and Precautions: must be prepared and transferred under inert gas (Ar or N2) to exclude oxygen and moisture.

Wittig Reaction.

Allylidenetriphenylphosphorane usually reacts at the a-carbon with aldehydes to give a mixture of (E)- and (Z)-1,3-dienes directly in good yield (eq 1).2 This process has been utilized for synthesis of an intermediate of leukotriene B4 (eq 2).15 The Wittig reaction with ketones occurs at higher temperature (eq 3).16 In contrast, the g-substitution product is preferentially formed in the condensation with aldehydes, when allylidenetriphenylphosphorane is generated with DBU in refluxing methanol.17

Structurally related allylidenetriphenylphosphoranes have been widely employed for the Wittig alkenation reaction.11-13 Reaction of (E)-2-octenylidenetriphenylphosphorane with acrolein gives a 3:2 mixture of (E)- and (Z)-trienes (eq 4).11 In this reaction the geometry of the starting (E)-2-octenylphosphonium bromide is preserved during both ylide formation and subsequent reaction with aldehyde.

The stereochemistry of the Wittig alkenation of aldehydes with allylic phosphorus ylides has been extensively studied by Tamura et al.18 Selective synthesis of (Z)-1,3-dienes has been achieved by the condensation of an allyltitanium reagent, generated from allyldiphenylphosphine, with aldehydes19 (for synthesis of (E)-1,3-dienes, see also Allyldiphenylphosphine Oxide).

Conjugate Addition.

Allylidenetriphenylphosphorane reacts with an enone to give a cyclic 1,3-diene (eq 5).3,20 In this reaction the addition of the g-position of the ylide to the b-carbon of the enone occurs first, and then the generated ylide (1) undergoes an intramolecular Wittig condensation to produce the 1,3-diene. Strained bridgehead alkene (2) has been also successfully synthesized by this method.20b In contrast, reaction with a b-chloro-a,b-unsaturated ketone followed by treatment with benzaldehyde yielded triene (3).21

Other Reactions.

Addition of allylidenetriphenylphosphorane to benzyne and subsequent treatment with HBr affords cinnamylphosphonium bromide.22 Silylation with Chlorotrimethylsilane occurs regiospecifically at the g-position.23 Reaction with isocyanate gives 3-pyridylidenephosphorane.24

1. (a) Maercker, A. OR 1965, 14, 270. (b) Bestmann, H. J.; Zimmermann, R. Organic Phosphorus Compounds; Kosolapoff, G. M., Maier, L., Eds.; Wiley-Interscience: New York, 1972; Vol. 3, pp 1-183. (c) Larock, R. C. Comprehensive Organic Transformations; VCH: New York, 1989; pp 173-184. (d) Maryanoff, B. E.; Reitz, A. B. CRV 1989, 89, 863.
2. Wittig, G.; Schöllkopf, U. CB 1954, 87, 1318.
3. Büchi, G.; Wüest, H. HCA 1971, 54, 1767.
4. (a) Albright, T. A.; Gordon, M. D.; Freeman, W. J.; Schweizer, E. E. JACS 1976, 98, 6249. (b) Schlosser, M.; Lehmann, R.; Jenny, T. JOM 1990, 389, 149.
5. (a) Bassi, I. W.; Scordamaglia, R. JOM 1973, 51, 273. (b) Greco, A.; Scordamaglia, R. Chim. Ind. (Milan) 1973, 55, 241.
6. Arnett, E. M.; Wernett, P. C. JOC 1993, 58, 301.
7. Okada, K.; Nozaki, M.; Takashima, Y.; Nakatani, N.; Nakatani, Y.; Matsui, M. ABC 1977, 41, 2205.
8. Davies, D. L.; Knox, S. A. R.; Mead, K. A.; Morris, M. J.; Woodward, P. JCS(D) 1984, 2293.
9. Schlosser, M.; Schaub, B. C 1982, 36, 396.
10. Ipaktschi, J.; Saadatmandi, A. LA 1984, 1989.
11. Näf, F.; Decorzant, R.; Thommen, W.; Willhalm, B.; Ohloff, G. HCA 1975, 58, 1016.
12. Boland, W.; Schroer, N.; Sieler, C.; Feigel, M. HCA 1987, 70, 1025.
13. Lubineau, A.; Augé, J.; Lubin, N. JCS(P1) 1990, 3011.
14. Bogdanovic, B.; Konstantinovic, S. S 1972, 481.
15. (a) Mills, L. S.; North, P. C. TL 1983, 24, 409. (b) Corey, E. J.; Marfat, A.; Goto, G.; Brion, F. JACS 1980, 102, 7984.
16. Tobe, Y.; Kishimura, T.; Kakiuchi, K.; Odaira, Y. JOC 1983, 48, 551.
17. Vedejs, E.; Bershas, J. P.; Fuchs, P. L. JOC 1973, 38, 3625.
18. (a) Tamura, R.; Kato, M.; Saegusa, K.; Kakihana, M.; Oda, D. JOC 1987, 52, 4121. (b) Tamura, R.; Saegusa, K.; Kakihana, M.; Oda, D. JOC 1988, 53, 2723.
19. (a) Ukai, J.; Ikeda, Y.; Ikeda, N.; Yamamoto, H. TL 1983, 24, 4029. (b) Ikeda, Y.; Ukai, J.; Ikeda, N.; Yamamoto, H. T 1987, 43, 723.
20. (a) Dauben, W. G.; Hart, D. J.; Ipaktschi, J.; Kozikowski, A. P. TL 1973, 4425. (b) Dauben, W. G.; Ipaktschi, J. JACS 1973, 95, 5088.
21. Vedejs, E.; Bershas, J. P. TL 1975, 1359.
22. Zbiral, E. M 1967, 98, 916.
23. Shen, Y.; Wang, T. TL 1990, 31, 543.
24. Capuano, L.; Willmes, A. LA 1982, 80.

Akira Yanagisawa & Hisashi Yamamoto

Nagoya University, Japan

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