Allyltriphenylphosphonium Bromide1

[1560-54-9]  · C21H20BrP  · Allyltriphenylphosphonium Bromide  · (MW 383.27)

(conjugate diene-forming reagent, ring-forming reagent1)

Alternate Name: 2-propenyltriphenylphosphonium bromide.

Physical Data: mp 225-227 °C; pKa;3a 1H,4a 13C,4b 31P NMR spectra;4b MS;5 X-ray PES spectra.6

Solubility: sol acetonitrile; distribution of (1) between water and organic solvents.3b

Form Supplied in: white powder, mp 222-225 °C.

Handling, Storage, and Precautions: hygroscopic, irritant. Use in a fume hood.

Preparation of allyltriphenylphosphonium bromide (1)1 was accomplished by allowing Allyl Bromide to react with Triphenylphosphine in benzene.2 A couple of drops of methanolic Benzyltrimethylammonium Hydroxide2c or Triethylamine2d in refluxing acetonitrile converts (1) into 1-propenyltriphenylphosphonium bromide (2) (eq 1).2c,d

The first alkenation reaction was accomplished using Phenyllithium as the base to convert (1) into the phosphorane (3)2a followed by benzaldehyde to give a 50:50 (E):(Z) ratio of (4) (eq 2).2a

The preparation of phosphorane (3) for use in alkenation reactions has been accomplished using a large number of base/solvent pairs, such as PhLi/Et2O,2 n-Butyllithium/hexane,7 n-BuLi/Et2O,8a,b n-BuLi/THF,8c Methyllithium/Et2O,8d LiOEt/EtOH,9 Potassium Carbonate/toluene,10 and 1,8-Diazabicyclo[5.4.0]undec-7-ene/THF11 (the latter has been used on the fluoroborate, instead of the bromide salt). The aldehyde, in a gaseous state, has also been passed over a solid bed of K2CO3 mixed with the phosphonium salt (1) suspended in Carbowax 6000 at 150 °C.12 In a few cases the species used as the base has also contained an aldehydic function, which undergoes the Wittig alkenation reaction and then cyclizes,13 such as the reaction of (1) with sodiopyrrolaldehyde (eq 3).13a

Addition-elimination followed by the alkenation reaction has been accomplished with the nucleophilic site on (3) being the g-position (eq 4).14

Rings have been formed in reasonable yields via a variety of sequences, such as g-addition of (3) followed by reylidation and the Wittig reaction (eq 5),15 g-addition followed by cyclization and proton transfer (eq 6),16 and alkenation followed by electrocylization (eq 7).17

Although this last example is depicted as a Wittig alkenation reaction followed by electrocyclization, it is possible that, as with the example illustrated by eq 5,15 the reaction involves a g-addition followed by reylidation and then Wittig alkenation. There is an example of a Wittig alkenation of a ketonic function (a cyclohexanone moiety) by (3);8b however, there are numerous cases where a compound containing both aldehydic and ketonic functional groups only yields a product from the reaction of the former group.7c,8d,8e The ylide (3) is generally too stable to react with ketones.

The dianionic phosphonium species (or ylidic anion) (8) has been formed by treating (1) with 2 equiv of n-BuLi. Reaction with a carbonyl followed by aqueous acid quenching gives a product which arises from g-addition and alkenation (eq 8).7n

Addition of methyldichlorosilane to the double bond of (1) has been observed (eq 9).18 Some high-yield syntheses of p-allylphosphonium ylide complexes have been reported.19

With respect to the geometric isomerism of alkenes formed from (3), no definitive studies have been undertaken. However, the majority of the products reported gave (Z):(E) ratios ranging from 60:40 to 100% (Z).7a,7d,7e,7h,7i,7l,8e,13b,13d,20 Three papers reported (Z):(E) ratios near10 or at 1.2a,21 A few papers reported (Z):(E) ratios around 40:607f,8a,12,22,23 or smaller.11 Altering the solvent polarity was said to change the (Z):(E) ratio from 20:80 to 70:30; however, no details were reported.8a

Related Reagents.

Allyldiphenylphosphine Oxide.

1. (a) Bestmann, H. J.; Vostrowsky, O. Top. Curr. Chem. 1983, 109, 85. (b) Maercker, A. OR 1965, 14, 270. (c) Schöllkopf, U. AG 1959, 711, 260.
2. (a) Wittig, G.; Schöllkopf, U. CB 1954, 87, 1318. (b) Grayson, M.; Keough, P. T. JACS 1960, 82, 3919. (c) Keough, P. T.; Grayson, M. JOC 1964, 29, 631. (d) Swan, J. M.; Wright, S. H. B. AJC 1971, 24, 777.
3. (a) Ling-Chung, S.; Sales, K. D.; Utley, J. H. P. CC 1990, 662. (b) Gibson, N. A.; Weatherburn, D. C. Anal. Chim. Acta 1972, 58, 159.
4. (a) Seyferth, D.; Fogel, J. JOM 1966, 6, 205. (b) Albright, T. A.; Freeman, W. J.; Schweizer, E. E. JACS 1975, 97, 2946.
5. Wood, G. W.; McIntosh, J. M.; Lau, P. Y. JOC 1975, 40, 636.
6. Swartz, W. E. Jr.; Hercules, D. M. Anal. Chem. 1971, 43, 1066.
7. (a) Sodeoka, M.; Yamada, H.; Shibasaki, M. JACS 1990, 112, 4906. (b) Herczegh, P.; Zsély, M.; Szilagyi, L.; Dinya, Z.; Bognar, R. T 1989, 45, 5995. (c) Watanabe, Y.; Iida, H.; Kibayashi, C. JOC 1989, 54, 4088. (d) Herczegh, P.; Zsély, M.; Szilágyi, L.; Batta, G.; Bajza, I.; Bognar, R. T 1989, 45, 2793. (e) Hanessian, S.; Botta, M. TL 1987, 28, 1151. (f) Mori, K.; Gupta, A. K. T 1985, 41, 5295. (g) Hoffmann, R. W.; Riemann, A.; Mayer, B. CB 1985, 118, 2493. (h) Takeda, K.; Shibata, Y.; Sagawa, Y.; Urahata, M.; Funaki, K.; Hori, K.; Sasahara, H.; Yoshii, E. JOC 1985, 50, 4673. (i) Iida, H.; Tanaka, M.; Kibayashi, C. JOC 1984, 49, 1909. (j) Jain, S. C.; Dussourd, D. E.; Conner, W. E.; Eisner, T.; Guerrero, A.; Meinwald, J. JOC 1983, 48, 2266. (k) Padwa, A.; Chou, C. S.; Rieker, W. F. JOC 1980, 45, 4555. (l) Rosen, B. I.; Weber, W. P. JOC 1977, 42, 47. (m) Radcliffe, M. M.; Weber, W. P. JOC 1977, 42, 297. (n) Shen, Y.; Wang, T. TL 1991, 32, 4353.
8. (a) Nesbitt, B. F.; Beevor, P. S.; Cole, R. A.; Lester, R.; Poppi, R. G. TL 1973, 4669. (b) Inhoffen, H. H.; Quinkert, G.; Schütz, S. CB 1957, 90, 1283. (c) Smith, M. B.; Kwon, T. W. SC 1992, 22, 2865. (d) Ihara, M.; Kawaguchi, A.; Ueda, H.; Chihiro, M.; Fukumoto, K.; Kametani, T. JCS(P1) 1987, 1331. (e) Ando, T.; Casida, J. E. J. Agric. Food Chem. 1983, 31, 151.
9. Baldry, P. J. JCS(P2) 1980, 805.
10. Attra, T. B.; Le Bigot, Y.; El Gharbi, R.; Delmas, M.; Gaset, A. SC 1992, 22, 1421.
11. Vedejs, E.; Bershas, J. P.; Fuchs, P. L. JOC 1973, 38, 3625.
12. Angeletti, E.; Tundo, P.; Venturello, P. CC 1983, 269.
13. (a) Schweizer, E. E.; Light, K. K. JOC 1966, 31, 2912. (b) Schweizer, E. E.; Shaffer, E. T.; Hughes, C. T.; Berninger, C. J. JOC 1966, 31, 2907. (c) Schweizer, E. E.; Berninger, C. J. CC 1965, 92. (d) Hug, R.; Hansen, H.-J.; Schmid, H. HCA 1972, 55, 1828.
14. (a) Vedejs, E.; Bershas, J. P. TL 1975, 1359. (b) Carsky, P.; Hünig, S.; Stemmler, I.; Scheutzow, D. LA 1980, 291.
15. (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.
16. Ipaktschi, J.; Saadatmandi, A. LA 1984, 1989.
17. Büchi, G.; Wüest, H. HCA 1971, 54, 1767.
18. Brovko, V. S.; Skvortsov, N. K.; Ivanov, A. Y.; Reikhsfel'd, V. O. ZOB 1983, 53, 1831.
19. (a) Itoh, K.; Nishiyama, H.; Ohnishi, T.; Ishii, Y. JOM 1974, 76, 401. (b) Greco, A. JOM 1972, 43, 351. (c) Starzewski, K. A. O.; Dieck, H. T.; Franz, K. D.; Hohmann, F. JOM 1972, 42, C35.
20. Näf, F.; Decorzant, R.; Thommen, W.; Willhalm, B.; Ohloff, G. HCA 1975, 58, 1016.
21. Naruta, Y.; Nagai, N.; Arita, Y.; Maruyama, K. JOC 1987, 52, 3956.
22. Iida, H.; Tanaka, M.; Kibayashi, C. CC 1983, 1143.
23. Alberola, A.; Alonso, F.; Cuadrado, P.; Sañudo, M. C. JHC 1988, 25, 235.

Edward E. Schweizer

University of Delaware, Newark, DE, USA

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