(2-Bromovinyl)trimethylsilane

[13682-94-5]  · C5H11BrSi  · (2-Bromovinyl)trimethylsilane  · (MW 179.13) (E)

[41309-43-7] (Z)

[70737-20-1]

(for introduction of the b-(trimethylsilyl)vinyl moiety; the resulting alkenylsilanes undergo useful electrophilic substitutions of the TMS group1)

Alternate Name: 1-bromo-2-trimethylsilylethylene.

Physical Data: (E)-isomer: bp 54-55 °C/56 mmHg; d 1.16 g cm-3. (Z)-isomer: bp 50-52 °C/56 mmHg.

Form Supplied in: (E)-isomer, typically containing ca. 10% (Z)-isomer.

Analysis of Reagent Purity: 1H NMR (CH=CH) of (E)-isomer: d 6.48 (s); (Z)-isomer: d 6.35, 6.50, 6.86, 7.01 (AB pattern, J = 9 Hz).

Preparative Methods: (E)-isomer: by the sequence of eq 1,2 or more directly from the readily available Vinyltrimethylsilane3 (eq 2).4 (Z)-isomer: by bromination-debromosilylation of 1,2-bis(trimethylsilyl)ethylene (eq 3).5

Purification: An 87:13 (E):(Z) mixture was enriched to 98-99% (E) by fractionation.6

Handling, Storage, and Precautions: use in a fume hood.

Introduction.

Methods for the introduction of the b-(trimethylsilyl)vinyl moiety into organic frameworks using (2-bromovinyl)trimethylsilane (1) may be grouped into two broad categories: those which employ (1) as an electrophilic component, or organometallic derivatives of (1) as nucleophilic reaction components.

As Nucleophilic Component.

The first such reagent7 prepared from (1) was (E)-b-(trimethylsilyl)vinylmagnesium bromide (2) (eq 4).2 This undergoes expected reactions with a number of electrophiles (eqs 5-8)2,8,9 as well as coupling with (1) (eq 9).10

In addition, coupling of the Grignard (2) with both alkenyl and alkyl halides has been promoted by metal ion catalysis (eqs 10-12).5,11 Under copper(I) catalysis, (2) reacts with conjugated enones in a 1,4-fashion (eq 13),11,12 and the diorganocuprate derived from (2) behaves in a similar fashion (eq 14).13

As Electrophilic Component.

Although an example of coupling between (1) and a lithium diorganocuprate is known (eq 15),14 most substitution reactions of this nature employ palladium catalysis. In this way, organomagnesium (eq 16),11 as well as organozinc (eqs 17 and 18),15,16 alkynyltin (eq 19),15b and alkenylaluminum compounds (eq 20)15 have been effectively used as coupling agents. Although the commonly available 9:1 (E)/(Z) mixture of (1) was utilized in these couplings, the alkenylsilane products were obtained in high stereoisomeric (E) purity.15 The cross-coupling of an alkenylzinc reagent with (1) was used for a direct synthesis of a dihydrobenzisoquinoline (eq 21).17

Couplings of more highly ionic organometallic coreactants with (1) have also proven amenable to palladium catalysis. These procedures are often tolerant of accompanying electrophilic functionalities (eqs 22 and 23).18,19 Palladium catalysis has also been utilized for the formation of (E)-b-(trimethylsilyl)vinyl sulfides from (1) (eq 24).20 A stereoisomeric purity of >99% was observed for the product. Although (1) has generally been found to be much more reactive than its (Z)-isomer (3) is cross-coupling reactions,15,20 the latter has been efficiently employed in the stereospecific transformation of eq 25.21

In behavior separate from those described above, (3) undergoes electrophilic substitution of the TMS group characteristic of alkenylsilanes1 when treated with acyl chloride-Aluminum Chloride mixtures (eq 26).5

Related Reagents.

(E)-1-Lithio-2-tributylstannylethylene; (E)-2-(Trimethylsilyl)vinyllithium.


1. Alkenylsilane chemistry reviews: (a) Fleming, I.; Dunogues, J.; Smithers, R. OR 1989, 37, 57. (b) Blumenkopf, T. A.; Overman, L. E. CRV 1986, 86, 857. (c) Colvin, E. W. Silicon in Organic Synthesis; Butterworths: London, 1981.
2. Mironov, V. F.; Petrov, A. D.; Maksimova, N. G. BAU 1959, 1864.
3. Holmes, A. B.; Sporikou, C. N. OS 1987, 65, 61.
4. (a) Boeckman, Jr., R. K.; Bruza, K. J. JOC 1979, 44, 4781. (b) Yarosh, O. G.; Voronov, V. K.; Kamarov, N. V. BAU 1971, 795.
5. Pillot, J.-P.; Dunogues, J.; Calas, R. SC 1979, 9, 395. Thermal isomerization of the (Z)-isomer (180 °C, 16 h) afforded an 18:82 (Z)/(E) mixture.
6. Fiandanese, V.; Marchese, G.; Mascolo, G.; Naso, F.; Ronzini, L. TL 1988, 29, 3705.
7. Also see (E)-2-(Trimethylsilyl)vinyllithium.
8. Brook, A. G.; Duff, J. M. CJC 1973, 51, 2024.
9. (a) Denmark, S. E.; Habermas, K. L.; Hite, G. A.; Jones, T. K. T 1986, 42, 2821. (b) Denmark, S. E.; Jones, T. K. HCA 1983, 66, 2377. (c) Denmark, S. E.; Jones, T. K. JACS 1982, 104, 2642.
10. Bock, H.; Seidl, H. JACS 1968, 90, 5694.
11. Huynh, C.; Linstrumelle, G. TL 1979, 1073.
12. Han, Y. K.; Paquette, L. A. JOC 1979, 44, 3731.
13. Denmark, S. E.; Germanas, J. P. TL 1984, 25, 1231.
14. Koshutin, V. I.; Nazarenko, N. P. JGU 1982, 52, 2115.
15. (a) Andreini, B. P.; Carpita, A.; Rossi, R. TL 1988, 29, 2239. (b) Andreini, B. P.; Carpita, A.; Rossi, R.; Scamuzzi, B. T 1989, 45, 5621.
16. Ennis, D. S.; Gilchrist, T. L. T 1990, 46, 2623.
17. Gilchrist, T. L.; Healy, M. A. M. TL 1990, 31, 5807.
18. Clark, D. L.; Chou, W. N.; White, J. B. JOC 1990, 55, 3975.
19. Cazes, B.; Colovray, V.; Gore, J. TL 1988, 29, 627.
20. Carpita, A.; Rossi, R.; Scamuzzi, B. TL 1989, 30, 2699.
21. Arsequell, G.; Camps, F.; Fabrias, G.; Guerrero, A. TL 1990, 31, 2739.

Robert F. Cunico

Northern Illinois University, DeKalb, IL, USA



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