Trimethylsilylallyllithium1

[67965-38-2]  · C6H13LiSi  · Trimethylsilylallyllithium  · (MW 120.22)

(addition to ketones and aldehydes;2 synthesis of dienes with defined stereochemistry;3 reaction with alkyl halides,4 epoxides,5 and other electrophiles6)

Alternate Name: [1-(trimethylsilyl)-2-propenyl]lithium.

Physical Data: 1H and 13C NMR solution studies of the TMEDA complex in THF7a and the X-ray structure of the TMEDA complex of a closely related reagent have been reported.7b

Solubility: sol THF, ether.

Preparative Method: prepared in situ, under an inert atmosphere, by reaction of Allyltrimethylsilane with n-Butyllithium or with s-Butyllithium.1,7a

Handling, Storage, and Precautions: solutions are inflammable. Preclude contact of the solutions with air and moisture.

Addition to Ketones and Aldehydes.2

Trimethylsilylallyllithium (1) adds to most aldehydes and ketones to give g-(E)-vinylsilanes (eq 1) and only very small amounts of a-condensation products or Peterson elimination products.2 The stereoselectivity has been investigated by NMR studies carried out in solution, which show that (1) exists exclusively in the exo conformation.7

However, other types of silylallyllithium compounds with internal complexing capabilities are suspected to exist in the endo conformation under certain conditions. For example, (dialkylaminomethyl)dimethylsilylallyllithiums give the usual g-(E)-vinylsilane products with reasonable selectivity when they react with aldehydes and ketones in toluene. However, if a small amount of 1,2-dimethoxyethane is added to the reagent, the stereoselectivity of the reaction is reversed, giving the g-(Z)-vinylsilane as the major product (eq 2).8

These g-condensation products are useful in organic synthesis. For example, the vinylsilane portion of the molecule can be used as an internal nucleophile in cyclization reactions, as demonstrated in the synthesis of substituted aromatic compounds (eq 3).9 They can also be used as lactone precursors (eq 4), as demonstrated in the synthesis of the steroidal 17-spiro-g-lactone (2).2

The reactivity of the double bond in these hydroxyvinylsilane products is affected by the trimethylsilyl group. The reaction of (3) with N-Bromosuccinimide leads to the formation of a b-bromooxetane at 0 °C or of a diene product at 40 °C (eq 5). The expected formation of the tetrahydrofuran product has not been observed.2

Synthesis of Dienes with Defined Stereochemistry.3

The normal g-regioselectivity in the reaction of (1) with ketones and aldehydes can be modified by the use of other metal counter-ions. Thus a-substitution products can be obtained selectively if Magnesium Bromide or other Lewis acids are added to the reaction media (eq 6). The resulting alcohols are also diastereomerically enhanced. These observations are explained by the formation of a six-membered ring transition state (4) where the metal ion M+ coordinates with the carbonyl oxygen. Other reagents used to control the regio- and stereoselectivity of the reactions of (1) with aldehydes are shown in eq 7.2c,3c-g The alcohols are useful for the stereospecific formation of dienes by the Peterson alkenation reaction (eq 6).3a The same logical approach has been used to obtain (E)- or (Z)-4-aryl (or alkyl)-(E)-1-(trimethylsilyl)-1,3-butadienes from the deprotonation of 1,3-bis(trimethylsilyl)propene, an a-trimethylsilylated equivalent of (1), and reaction with benzaldehyde (eq 8).3b

Reaction with Alkyl Halides, Epoxides, and Other Electrophiles.4-6

Trimethylsilylallyllithium reacts with alkyl halides at low temperature, giving mixtures of a- and g-(E) products in ratios that vary with the electrophile and the reaction conditions (eq 9).4 In these reactions the g-(E)-alkylation product generally predominates. For example, when trimethylsilylallyllithium is formed by deprotonation of allyltrimethylsilane with n-butyllithium in the presence of potassium t-butoxide in THF, the (E)-vinylsilane alkylation product is obtained in better then 85% yield (eq 10). This has been exploited in the synthesis of (Z)-9-tricosene epoxide, the sex pheromone of the gypsy moth.4a

This g-regioselectivity can be further improved by the use of bulky substituents attached to the silicon atom.4a,b In recent years, attempts have been made at developing reagents closely related to trimethylsilylallyllithium that will permit a-alkylation in high regio- and diastereoselectivity. In some instances, significant changes in regioselection can be achieved once the silicon is substituted with alkoxy or aminomethyl groups.4c,4e In particular, the use of chiral, lithium-chelating, amino groups attached to silicon as shown in eq 11, has been successfully applied to the regio- and diastereoselective alkylation of allylsilanes.4c,e This same approach gives even better results in the synthesis of chiral propargylic alcohols (eq 12).4d

Trimethylsilylallyllithium reacts with epoxides (at -40 °C in THF for 2 h) to give alcohols in good yields. Highest a-selectivity is obtained with smaller monosubstituted epoxides; larger trisubstituted epoxides give g-products. In unsymmetrical epoxides, attack is on the less hindered side5a with the notable exception of trimethylsilyl-substituted ones, where the attack occurs predominantly on the carbon bearing the trimethylsilyl group. This approach has been used to synthesize 1-silyl-substituted 1,4-dienes (eq 13).5b Trimethylsilylallyllithium also reacts with many other electrophiles including imines,6a carbon dioxide,6b substituted naphthalene,6c selenocyanogen,6d and dimethylformamide.2a

Related Reagents.

The literature contains numerous examples of reagents having different substitutions on the silicon moiety. The introduction of bulky and/or aromatic groups on the silicon atom, for example in (5) (R = Ph, p-tolyl, vinyl, t-Bu),6b (6),6b and (7) (R = OMe, Ph, Et, i-Pr),2a,4a,6b,10 has been used to modify the reactivity of the allylic anion. The influence exerted by these groups is mediated through their steric and/or electronic interactions with the allylic anion and with its counter ion. It is not surprising then that the presence of chelating amino or ether functions on the silicon atom, for example in (5) [R = NEt2, N(i-Pr)2, NH(CH2CH2NMe2), pyrrolidino, CH2(methoxymethylpyrrolidine), CH2N(CH2CH2OMe)2], also modifies the reactivity of the allyllithium attached to it.4c,11 The silylallyllithium reagents are normally obtained by deprotonation of the corresponding allylsilanes. However, g-deprotonation of vinylsilanes can also be used for the same purposes, as is the case when either (8) or (9) are used to give the corresponding silylallyllithium reagent.12 Other reagents (10)-(17) having heteroatom substituents on the allyl group have also been used.3b,7b,13-19

A few carbon-substituted reagents (18)-(20) have also been prepared.4b,6b,20 Of these, reagent (18) has been used in the synthesis of frontalin, a natural product. The last three examples (21)-(23) show interesting steric and electronic effects on the regio- and stereoselectivity of the alkylation and condensation reactions.4e,21,22

Related Reagents.

Allyllithium; Crotyllithium; 9-[1-(Trimethylsilyl)-2(E)-butenyl]-9-borabicyclo[3.3.1]nonane; 5-Trimethylsilyl-1,3-pentadiene.


1. For reviews, see; Colvin, E. W. Silicon in Organic Synthesis; Butterworths: London, 1981; p 118. Weber, W. P. Silicon Reagents for Organic Synthesis; Springer: Berlin, 1983; p 199, and references cited therein.
2. (a) Corriu, R. J. P.; Masse, J.; Samate, D. JOM 1975, 93, 71. (b) Ehlinger, E.; Magnus, P. TL 1980, 21, 11; Ehlinger, E.; Magnus, P. JACS 1980, 102, 5004, and references cited therein. (c) Corriu, R. J. P.; Guerin, C.; M'Boula, J. TL 1981, 22, 2985.
3. (a) Lau, P. K. W.; Chan, T. H. TL 1978, 19, 2383. (b) Chan, T. H.; Li. J. S. CC 1982, 969; Carter, M. J.; Fleming, I. CC 1976, 679; Carter, M. J.; Fleming, I.; Percival, A. JCS(P1) 1981, 2415; Corriu, R.; Escudie, N.; Guerin, C. JOM 1984, 264, 207. (c) Wakamatsu, K.; Oshima, K.; Utimoto, K. CL 1987, 2029. (d) Yamamoto, Y.; Saito, Y.; Maruyama, K. CC 1982, 1326; Yamamoto, Y.; Saito, Y.; Maruyama, K. JOM 1985, 292, 311, and references cited therein; Hoffmann, R. W.; Brinkmann, H.; Frenking, G. CB 1990, 123, 2387; Tsai. D. J. S.; Matteson, D. S. TL 1981, 22, 2751. (e) Yamamoto, Y.; Yatagai, H.; Saito, Y.; Maruyama, K. JOC 1984, 49, 1096; Naruta, Y.; Uno, H.; Maruyama, K. CL 1982, 961. (f) Sato, F.; Suzuki, Y.; Sato, M. TL 1982, 23, 4589. (g) Reetz, M. T.; Wenderoth, B. TL 1982, 23, 5259; Reetz, M. T.; Steinbach, R.; Westermann, J.; Peter, R.; Wenderoth, B. CB 1985, 118, 1441; Ikeda, Y.; Yamamoto, H. BCJ 1986, 59, 657.
4. (a) Chan, T. H.; Koumaglo, K. JOM 1985, 285, 109; Koumaglo, K.; Chan, T. H. TL 1984, 25, 717. (b) Li, L. H.; Wang, D.; Chan, T. H. TL 1991, 32, 2879; Chan, T. H.; Chen, L. M.; Wang, D.; Li, L. H. CJC 1993, 71, 60. (c) Horvath, R. F.; Chan, T. H. JOC 1989, 54, 317; Lamothe, S.; Cook, K. L.; Chan, T. H. CJC 1992, 70, 1733. (d) Hartley, R. C.; Lamothe, S.; Chan, T. H. TL 1993, 34, 1449. (e) Lamothe, S.; Chan, T. H. TL 1991, 32, 1847.
5. (a) Schaumann, E.; Kirschning, A. TL 1988, 29, 4281. (b) Schaumann, E.; Kirschning, A. JCS(P1) 1990, 419; Kirschning, A.; Narjes, F.; Schaumann, E. LA 1991, 933. See also ref 1.
6. (a) Guyot, B.; Pornet, J.; Miginiac, L. SC 1990, 20, 2409. (b) Uno, H. BCJ 1986, 59, 2471; Naruta, Y.; Uno, H.; Maruyama, K. CL 1982, 961. (c) Gant, T. G.; Meyers, A. I. JACS 1992, 114, 1010. (d) Meinke, P. T.; Krafft, G. A.; Guram, A. JOC 1988, 53, 3632.
7. (a) Fraenkel, G.; Chow, A.; Winchester, W. R. JACS 1990, 112, 2582, and references cited therein. (b) Boche, G.; Fraenkel, G.; Cabral, J.; Harms, K.; van Eikema Hommes, N. J. R.; Lohrenz, J.; Marsch, M.; von Ragué Schleyer, P. JACS 1992, 114, 1562.
8. Chan, T. H.; Labrecque, D. TL 1992, 33, 7997. Similar results are obtained with boronate complexes; see: Tsai, D. J. S.; Matteson, D. S. OM 1983, 2, 236.
9. Tius, M. A. TL 1981, 22, 3335.
10. Muchowski, J. M.; Naef, R.; Maddox, M. L. TL 1985, 26, 5375.
11. Tamao, K.; Nakajo, E.; Ito, Y. T 1988, 44, 3997; see also Refs. 4b and 4c.
12. Wakamatsu, K.; Oshima, K.; Utimoto, K. CL 1987, 2029.
13. Seyferth, D.; Mammarella, R. E. JOM 1978, 156, 279.
14. Ikeda, Y.; Furuta, K.; Meguriya, N.; Ikeda, N.; Yamamoto, H. JACS 1982, 104, 7663; Kyler, K. S.; Netzel, M. A.; Arseniyadis, S.; Watt, D. S. JOC 1983, 48, 383; Furuta, K.; Ikeda, Y.; Meguriya, N.; Ikeda, N.; Yamamoto, H. BCJ 1984, 57, 2781.
15. Murai, A.; Abiko, A.; Shimada, N.; Masamune, T. TL 1984, 25, 4951; Marsch, M.; Harms, K.; Zschage, O.; Hoppe, D.; Boche, G. AG(E) 1991, 30, 321.
16. Ukai, J.; Ikeda, Y.; Ikeda, N.; Yamamoto, H. TL 1984, 25, 5173; 1984, 25, 5177.
17. Trost, B. M.; Self, C. R. JACS 1983, 105, 5942.
18. Reich, H. J.; Clark, M. C.; Willis, W. W., Jr. JOC 1982, 47, 1618.
19. Degl'Innocenti, A.; Ulivi, P.; Capperucci, A.; Reginato, G.; Mordini, A.; Ricci, A. SL 1992, 883.
20. Mordini, A.; Palio, G.; Ricci, A.; Taddei, M. TL 1988, 29, 4991.
21. Sternberg, E.; Binger, P. TL 1985, 26, 301.
22. Yasuda, H.; Nishi, T.; Miyanaga, S.; Nakamura, A. OM 1985, 4, 359.

Denis Labrecque & Tak-Hang Chan

McGill University, Montreal, Quebec, Canada



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