Lithium Acetylide


[1111-64-4]  · C2HLi  · Lithium Acetylide  · (MW 31.97) (ethylenediamine complex)

[6867-30-7]  · C4H9LiN2  · Lithium Acetylide-Ethylenediamine  · (MW 92.09)

(reagent for addition of acetylene to ketones,1 opening of epoxides,2 and ethynylation of alkyl halides3)

Solubility: sol THF; LiC&tbond;CH.EDA sol alkyl amines, slightly sol THF.

Form Supplied in: lithium acetylide.EDA is supplied as a powder.

Preparative Method: monolithium lithium acetylide is prepared by treating a THF solution of Acetylene with n-Butyllithium at 78 °C (eq 1).1

It is critical to keep the temperature at -78 °C. The concentration should be 0.5 M or less. At higher concentrations and temperatures, a white precipitate forms (presumably Dilithium Acetylide) and yields of addition product fall appreciably. Properly formed, lithium acetylide in THF should be a clear, colorless solution.

Handling, Storage, and Precautions: lithium acetylide/THF solution must be used immediately after preparation. It decomposes above -78 °C. A saturated solution of THF/acetylene should not be used during the preparation of lithium acetylide since this may lead to an acetylene atmosphere above the THF. n-Butyllithium dropping through the acetylene atmosphere may react violently. Lithium acetylide is air and moisture sensitive.

Addition to Ketones.

Lithium acetylide rapidly adds to a variety of aldehydes and ketones (eq 2).1

Hindered ketones such as di-t-butyl ketone give best results if an excess of reagent is used. The reagent freshly prepared in THF generally gives better results than lithium acetylide.EDA4 or lithium acetylide in ammonia.5 In the case of easily enolizable ketones, the cerium reagent works well (eq 3).6

The TMS cerium acetylide reportedly gives better results than the unsubstituted cerium regent (eq 4).7

Reaction with Epoxides.

Lithium acetylide in THF decomposes before it can react with epoxides. However, in the presence of Boron Trifluoride Etherate epoxides are readily opened (eq 5).2

Lithium acetylide.EDA in THF/HMPA8 or DMSO9 may also be used to open epoxides (eq 6).

Ethynylation of Alkyl Halides.

Lithium acetylide.EDA in DMSO can be used to convert alkyl halides and sulfates into terminal alkynes (eq 7).3

Monolithium acetylide in THF in the presence of HMPA is stable at 0 °C. This reagent may also be used to ethynylate alkyl halides (eq 8).10

An alternative route to terminal alkynes involves iodination of lithium ethynyl trialkylborates (eq 9).11 These are prepared by treating a trialkylborane with lithium acetylide.EDA. This method retains the stereochemistry of the boron-carbon bond.

Related Reagents.

Dilithium Acetylide; Ethynylmagnesium Bromide; Lithium Chloroacetylide; Lithium (Trimethylsilyl)acetylide; Propynyllithium.

1. (a) Midland, M. M. JOC 1975, 40, 2250. (b) Midland, M. M.; McLoughlin, J. I., Werley, R. T. OS 1989, 68, 14. (c) Midland, M. M.; McLoughlin, J. I., Werley, R. T. OSC 1993, 8, 391.
2. Yamaguchi, M.; Hirao, I. CC 1984, 202.
3. Smith, W. N.; Beumel, O. F. S 1974, 441.
4. Beumel, O. F., Jr.; Harris, R. F. JOC 1964, 29, 1872.
5. Oroshnik, W.; Mebane, A. D. JACS 1949, 71, 2062.
6. Imamota, T.; Sugiura, Y.; Takiyama, N. TL 1984, 25, 4233.
7. Suzuki, M.; Kimura, Y.; Terashima, S. CPB 1986, 34, 1531.
8. Corey, E. J.; Kang, J. JACS 1981, 103, 4618.
9. Hanack, M.; Kunzmann, E.; Schumacher, W. S 1978, 26.
10. (a) Johnston, B. D.; Oehlschlager, A. C. JOC 1982, 47, 5384. (b) Beckmann, W.; Doerjer, G.; Logemann, E.; Merkel, C.; Schill, C.; Zürcher, C. S 1975, 423.
11. Midland, M. M.; Sinclair, J. A.; Brown, H. C. JOC 1974, 39, 731.

M. Mark Midland

University of California, Riverside, CA, USA

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