encyclopedia of reagents for organic synthesis || ethynylmagnesium bromide

ETHYNYLDIMETHYLALUMINUM 1 Ethynylmagnesium Bromide MgX (X = Br) [4301-14-8] C 2 HBrMg (MW 129.24) InChI = 1/C2H.BrH.Mg/c1-2;;/h1H;1H;/q;;+1/p-1/fC2H.Br.Mg/ h;1h;/q;-1;m/rC2HBrMg/c1-2-4-3/h1H InChIKey = HUGJUYPSXULVQQ-AECKLGIBCF (X = Cl) [65032-27-1] C 2 HClMg (MW 84.79) InChI = 1/C2H.ClH.Mg/c1-2;;/h1H;1H;/q;;+1/p-1/fC2H.Cl.Mg/ h;1h;/q;-1;m/rC2HClMg/c1-2-4-3/h1H InChIKey = YEWNLGTVYUADOR-DQAIVLDJCO (addition of acetylene to ketones; 1 preparation of TMSC≡CH 2 ) Preparative Methods: an Organic Synthesis preparation of ethynylmagnesium bromide 1 and chloride 2 from Acetylene and Ethylmagnesium Bromide or butylmagnesium chloride, respectively, is available. The use of butylmagnesium chloride instead of ethylmagnesium bromide is recommended 2 because of the greater solubility of the chloride. Handling, Storage, and Precautions: ethynylmagnesium halides are air and moisture sensitive. They are usually used immedi- ately 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≡CMgX than is monolithium acetylide. Lithium Acetylide provides the above product in 96% yield. 3 Ethynyl- magnesium chloride also adds to aldehydes (eq 2). 4 MgBr Ph H O Ph OH (1) 58–69% MgCl H O OH MeO OMe MeO OMe (2) 87% Preparation of TMS-acetylene. 2 Treatment of ethynylmagnesium chloride with Chlorotrimethylsilane provides a good route to Trimethylsilylacetylene (eq 3). (3) MgCl TMS + TMSCl 75% Related Reagents. Lithium Acetylide; Lithium Chloroacety- lide; Lithium (Trimethylsilyl)acetylide. 1. Skattebol, L.; Jones, E. R. H.; Whiting, M. S., Org. Synth., Coll. Vol. 1963, 4, 792. 2. Holmes, A. B.; Sporikou, C. N., Org. Synth., Coll. Vol. 1993, 8, 606. 3. Midland, M. M., J. Org. Chem. 1975, 40, 2250. 4. Descoins, C.; Henrick, C. A.; Siddall, J. B., Tetrahedron Lett. 1972, 3777. M. Mark Midland University of California, Riverside, CA, USA Avoid Skin Contact with All Reagents

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ETHYNYLDIMETHYLALUMINUM 1

Ethynylmagnesium Bromide

MgX

(X = Br)[4301-14-8] C2HBrMg (MW 129.24)InChI = 1/C2H.BrH.Mg/c1-2;;/h1H;1H;/q;;+1/p-1/fC2H.Br.Mg/

h;1h;/q;-1;m/rC2HBrMg/c1-2-4-3/h1HInChIKey = HUGJUYPSXULVQQ-AECKLGIBCF(X = Cl)[65032-27-1] C2HClMg (MW 84.79)InChI = 1/C2H.ClH.Mg/c1-2;;/h1H;1H;/q;;+1/p-1/fC2H.Cl.Mg/

h;1h;/q;-1;m/rC2HClMg/c1-2-4-3/h1HInChIKey = YEWNLGTVYUADOR-DQAIVLDJCO

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

Preparative Methods: an Organic Synthesis preparation ofethynylmagnesium bromide1 and chloride2 from Acetyleneand Ethylmagnesium Bromide or butylmagnesium chloride,respectively, is available. The use of butylmagnesium chlorideinstead of ethylmagnesium bromide is recommended2 becauseof the greater solubility of the chloride.

Handling, Storage, and Precautions: ethynylmagnesium halidesare air and moisture sensitive. They are usually used immedi-ately after preparation.

Addition to Ketones and Aldehydes.1 Ethynylmagnesiumbromide adds to ketones and aldehydes to give ethynyl carbinols(eq 1). The reagent is less prone to disproportionation toXMgC≡≡CMgX than is monolithium acetylide. LithiumAcetylide provides the above product in 96% yield.3 Ethynyl-magnesium chloride also adds to aldehydes (eq 2).4

MgBr

Ph H

OH(1)

58–69%

MgClH

O OH

MeO

OMe

MeO

OMe

(2)87%

Preparation of TMS-acetylene.2 Treatment of ethynyl-magnesium chloride with Chlorotrimethylsilane provides a goodroute to Trimethylsilylacetylene (eq 3).

(3)MgCl TMS+ TMSCl75%

Related Reagents. Lithium Acetylide; Lithium Chloroacety-lide; Lithium (Trimethylsilyl)acetylide.

1. Skattebol, L.; Jones, E. R. H.; Whiting, M. S., Org. Synth., Coll. Vol. 1963,4, 792.

2. Holmes, A. B.; Sporikou, C. N., Org. Synth., Coll. Vol. 1993, 8, 606.

3. Midland, M. M., J. Org. Chem. 1975, 40, 2250.

4. Descoins, C.; Henrick, C. A.; Siddall, J. B., Tetrahedron Lett. 1972, 3777.

M. Mark MidlandUniversity of California, Riverside, CA, USA

Avoid Skin Contact with All Reagents

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