Ethynylmagnesium Bromide

(X = Br)

[4301-14-8]  · C2HBrMg  · Ethynylmagnesium Bromide  · (MW 129.24) (X = Cl)

[65032-27-1]  · C2HClMg  · Ethynylmagnesium Chloride  · (MW 84.79)

(addition of acetylene to ketones;1 preparation of TMSC&tbond;CH2)

Preparative Methods: an Organic Synthesis preparation of ethynylmagnesium bromide1 and chloride2 from Acetylene and Ethylmagnesium Bromide or butylmagnesium chloride, respectively, is available. The use of butylmagnesium chloride instead of ethylmagnesium bromide is recommended2 because of the greater solubility of the chloride.

Handling, Storage, and Precautions: ethynylmagnesium halides are air and moisture sensitive. They are usually used immediately after preparation.

Addition to Ketones and Aldehydes.1

Ethynylmagnesium bromide adds to ketones and aldehydes to give ethynyl carbinols (eq 1). The reagent is less prone to disproportionation to XMgC&tbond;CMgX than is monolithium acetylide. Lithium Acetylide provides the above product in 96% yield.3 Ethynylmagnesium chloride also adds to aldehydes (eq 2).4

Preparation of TMS-acetylene.2

Treatment of ethynylmagnesium chloride with Chlorotrimethylsilane provides a good route to Trimethylsilylacetylene (eq 3).

Related Reagents.

Lithium Acetylide; Lithium Chloroacetylide; Lithium (Trimethylsilyl)acetylide.

1. Skattebol, L.; Jones, E. R. H.; Whiting, M. S. OSC 1963, 4, 792.
2. Holmes, A. B.; Sporikou, C. N. OSC 1993, 8, 606.
3. Midland, M. M. JOC 1975, 40, 2250.
4. Descoins, C.; Henrick, C. A.; Siddall, J. B. TL 1972, 3777.

M. Mark Midland

University of California, Riverside, CA, USA

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