[463-49-0]  · C3H4  · Allene  · (MW 40.07)

(used in photochemical, thermal, and transition metal mediated cycloadditions; precursor of allenyl- and propargyllithium; electrophile with cuprates)

Alternate Name: 1,2-propadiene.

Physical Data: mp -136 °C; bp -34 °C; flammable gas.

Solubility: insol H2O; sol THF, pet ether, benzene.

Form Supplied in: gas (lecture bottle); widely available.

Preparative Method: reaction of 2,3-Dichloropropene with Zinc in ethanol.1

Handling, Storage, and Precautions: flammable gas; handle in a fume hood.

Metalated Allenes.

Allene can be metalated at -70 °C to produce allenyllithium which reacts with alkyl halides to give high yields of terminal allenes (eq 1).2,3 Generally less than 5% of the alkyne is obtained. The dianion of allene can also be prepared and treated with electrophiles such as alkyl halides and carbonyl compounds (eqs 2 and 3).4-7 The regiochemistry of the alkylation is dependent on the choice of solvent: more coordinating solvents and solvent combinations typically provide the allene products6 while less polar solvents produce the substituted alkynes.4 The intermediate acetylides can be exposed to an additional electrophile to allow the formation of two new carbon-carbon bonds.3,7

Photochemical Cycloadditions.

Allene has been used extensively in intermolecular [2 + 2] photocycloaddition reactions.8 Cyclohexenones (eq 4),9 cyclopentenones (eq 5),10 and functionalized enones (eq 6)11 undergo cycloaddition with allene with excellent and predictable regioselectivity and in uniformly high yields. The stereochemistry of cycloaddition of allene to 4-substituted cyclohexenones has been interpreted by attack of allene on the enone excited state which is substantially pyramidalized at the b-carbon (eq 7).12,13

Thermal Cycloadditions.

Allene undergoes various thermal cycloadditions including thermal [2 + 2] cycloadditions (eq 8),14 Diels-Alder reactions (eq 9),15,16 and nitrone cycloadditions.17

Organometallic Catalyzed Reactions.

Allene reacts readily with Palladium(II) Chloride to form a p-allyl complex18 and many palladium catalyzed transformations of allene have been reported. Carbopalladation reactions provide ready access to 2-substituted 1,3-dienes (eq 10),19 bis-stannylation (eq 11) produces high yields of the vinylallylstannanes,20 and the analogous reaction with bis-silanes has been reported.21 Substituted acrylates and butenoates are available from the palladium catalyzed carbonylation of allene (eq 12).22

Nickel(II) catalysis has been utilized to prepare 4-methyl-4-pentenoic acid from allene23 and substituted allenes have been prepared from ketones by treatment with a titanacyclobutane (eq 13).24

Isopropenyl Stannanes, Silanes, and Germanes.

The reaction of allene with stannyl and silyl cuprates gives isopropenylsilanes25 and -stannanes26 (eqs 14 and 15) in excellent yield. Triphenylisopropenylgermane can be prepared from allene and triphenylgermane in the presence of Triethylborane.27 In addition, haloboration of allene with boron tribromide and anisole produces a 2-bromoallylboronate (eq 16),28 and electrophilic addition of phenylselenium bromide to allene provides 2-phenylselenoallyl bromide (eq 17).29

1. Cripps, H. N.; Kiefer, E. F. OSC 1973, 22.
2. Linstrumelle, G.; Michelot, D. CC 1975, 561.
3. Roumestant, M. L.; Arseniyadis, S.; Gore, J.; Laurent, A. CC 1976, 479.
4. (a) Hooz, J.; Calzada, J. G.; McMaster, D. TL 1985, 26, 271. (b) Hooz, J.; Cabezas, J.; Musmanni, S.; Calzada, J. OS 1990, 69, 120.
5. Michelot, D. SC 1989, 19, 1705.
6. Arseniyadis, S.; Gore, J.; Roumestant, M. L. T 1979, 35, 353.
7. Bartlett, W. R.; Johnson, W. S.: Plummer, M. S.; Small, V. R., Jr. JOC 1990, 55, 2215.
8. Crimmins, M. T.; Reinhold, T. L. OR 1993, 44, 297.
9. (a) Duc, D. M.; Fetizon, M.; Lazare, S. CC 1975, 282. (b) Duc, D. M.; Fetizon, M.; Hanna, I.; Lazare, S. S 1981, 139. (c) Paquette, L. A.; DeRussy, D. T.; Gallucci, J. C. JOC 1989, 54, 2278.
10. Magnus, P.; Slater, M. J.; Principe, L. M. JOC 1989, 54, 5148.
11. Kaneko, C.; Shimomura, N.; Momose, Y.; Naito, T. CL 1983, 1239.
12. Smith, A. B., III; Wexler, B. A.; Tu, C.-Y.; Konopelski, J. P. JACS 1985, 107, 1308.
13. (a) Wiesner, K. T 1975, 31, 1655. (b) Marini-Bettolo, G.; Sahoo, S. P.; Poulton, G. A.; Tsai, T. Y. R.; Wiesner, K. T 1980, 36, 719.
14. Bienfait, B.; Coppe-Motte, G.; Merenyi, R.; Viehe, H. G.; Sicking, W.; Sustmann, R. T 1991, 47, 8167.
15. Bonjouklian, R.; Ruden, R. A. JOC 1977, 42, 4095.
16. Fagan, P. J.; Burns, E. G.; Calabrese, J. C. JACS 1988, 110, 2979.
17. Tufariello, J. J.; Ali, S. A.; Kingele, H. O. JOC 1979, 44, 4215.
18. Schultz, R. G. T 1964, 20, 2809. Lupin, M. S.; Powell, J.; Shaw, B. L. JCS 1966, 1967.
19. (a) Gauthier, V.; Cazes, B.; Gore, J. TL 1991, 32, 915. (b) Kopola, N.; Friess, B.; Cazes, B.; Gore, J. TL 1989, 30, 3963.
20. Mitchell, T. N.; Kwetkat, K.; Rutschow, D.; Schneider, U. T 1989, 45, 969.
21. Watanabe, H. JOM 1982, 225, 343.
22. (a) Alper, H.; Hartstock, F. W.; Despeyroux, B. CC 1984, 905. (b) Tsuji, J.; Susuki, T. TL 1965, 3027.
23. Hoberg, H.; Peres, Y.; Krüger, C.; Tsay, Y. H. AG 1987, 99, 799.
24. Buchwald, S. L.; Grubbs, R. H. JACS 1983, 105, 5490.
25. (a) Fleming, I.; Rowley, M.; Cuadrado, P.; Gonzalez-Nogal, A. M.; Pulido, F. J. T 1989, 45, 413. (b) Barbero, A.; Cuadrado, P.; Gonzalez, A. M.; Pulido, F. J.; Fleming, I. JCS(P1) 1991, 2811; (c) Barbero, A.; Cuadrado, P.; Gonzalez, A. M.; Pulido, F. J.; Fleming, I. CC 1990, 1030. (d) Cuadrado, P.; Gonzalez, A. M.; Pulido, F. J. Fleming, I. TL 1988, 29, 1825.
26. Barbero, A.; Cuadrado, P.; Fleming, I.; Gonzalez, A. M.; Pulido, F. J. JCS(P1) 1992, 327.
27. Ichinose, Y.; Oshima, K.; Utimoto, K. BCJ 1988, 61, 2693.
28. Hara, S.; Suzuki, A. TL 1991, 32, 6749.
29. Halazy, S.; Hevesi, L. JOC 1983, 48, 5242.

Michael T. Crimmins

University of North Carolina, Chapel Hill, NC, USA

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