[10024-18-7]  · C3H3Br  · Bromoallene  · (MW 118.96)

(useful reagent for synthesis of terminal alkynic compounds2 and substituted allenes3)

Physical Data: bp 73 °C; d204 1.5508 g cm-3; n204 1.5212.

Solubility: sol most common organic solvents.

Form Supplied in: liquid; not available from common commercial suppliers.

Analysis of Reagent Purity: IR (cm-1): 3080, 3005, 1961, 1740, 1432, 1078, 862, 681, 603, 519.1 UV (nm (ε)): 269 (72), 192 (7780).1 1H NMR (ppm): 5.95 (t, 1H, J = 6 Hz), 4.93 (d, 2H, J = 6 Hz).4 13C NMR (ppm): 206.5, 86.8, 81.2.4

Preparative Methods: a tedious preparation5 of bromoallene by isomerization of propargyl bromide in the presence of copper(I) bromide has been improved6 and pure bromoallene can be obtained by removing the side product (propargyl bromide) with diethylamine (eq 1). Bromoallene has also been prepared by flash vacuum pyrolysis of bromocyclopropene4 or by phase transfer catalysis using CHBr(CH2Br2),7 but in both cases reaction mixtures contained a significant amount of propargyl bromide.

Bromoallene as an Electrophile.

The hydroalumination of 1-alkene followed by treatment with bromoallene in the presence of a catalytic amount of Copper(I) Chloride leads to terminal alkynic compounds (eq 2).2

This bromide was also subject to nucleophilic substitution by the anion of Ethyl Acetoacetate in a basic medium, but it was found that propargyl bromide (see Propargyl Chloride) gives identical results. A carbene mechanism was proposed (eq 3).8

Formation of substituted allenes by reaction of bromoallene with 1-alkynylzinc chlorides and a Pd0 catalyst is very useful. However, propargylic bromide or acetate can be used and seems more suitable for the preparation of unsymmetrical diallenes (e.g. R = t-BuCH=C=CH-) (eq 4).3

Bromoallene in Electrophilic Substitution via Metallic Derivatives.

Allenylmagnesium Bromide.

Although this compound was earlier prepared from propargyl bromide, bromoallene may be used to synthesize allenylmagnesium bromide. It has been well established that propargyl or allenyl bromide deliver the same allenyl Grignard derivative (eq 5).9

By a preferential attack at the 3-position (SE2 type mechanism), this organometallic gives exclusively or mainly the alkynic compound when added to most electrophiles in ether (eq 6).10 A reversal of reactivity may be encountered with polar aprotic solvents or with other organometallic compounds such as allenylzinc bromide (eq 7) or cadmium derivatives.10

The addition of CuI salts leads to allene products (eq 8).11


Bromoallene gives a [4 + 2] cycloaddition by reacting with hexachlorocyclopentadiene, leading to the 5-bromomethylene adduct (eq 9).12 A 1,3-dipolar cycloaddition with benzonitrile oxide13 as well as photochemical cycloadditions of 9,10-phenanthraquinones14 to bromoallene have also been investigated.

1. Landor, S. R., The Chemistry of the Allenes; Academic: London, 1982.
2. Sato, F; Kodama, H.; Sato, M. CL 1978, 789.
3. Ruitenberg, K.; Kleijn, H.; Elsevier, C. J.; Meijer, J.; Vermeer, P. TL 1981, 22, 1451.
4. Billups, W. E.; Bachman, R. E. TL 1992, 33, 1825.
5. Jacobs, T. L.; Brill, W. F. JACS 1953, 75, 1314.
6. Brandsma, L.; Verkruijsse, H. D. SC 1991, 21, 69.
7. Kurginyan, K. A.; Arakelova, S. V.; Kalaidzhyan, A. E. CA 1986, 105, 190 430x.
8. (a) Plouin, D.; Coeur, C.; Glénat, R. BSF 1974, 244. (b) Shiner, V. J. Jr.; Humphrey, J. S. Jr. JACS 1967, 89, 622.
9. Couffignal, R.; Gaudemar, M. BSF 1969, 3218.
10. (a) Moreau, J. L.; Gaudemar, M. BSF 1970, 2171. (b) Moreau, J. L.; Gaudemar, M. BSF 1970, 2175.
11. Bourgain-Commerçon, M.; Normant, J. F.; Villieras, J. JCR(S) 1977, 183.
12. Alexander, R.; Davies, D. I., JCS(C) 1971, 5.
13. Caristi, C.; Gattuso, M. JCS(P1) 1974, 679.
14. Boleij, J. S. M.; Bos, H. J. T. TL 1971, 3201.

Guy Fournet

Université Claude Bernard Lyon I, France

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