Ethylmagnesium bromide, reaction with alkynes

Acetylenic Grignard reagents are commonly prepared by reaction of the appropriate 1-alkyne with an alkyl Grignard reagent, such as ethylmagnesium bromide. 

Reactions of acetylene, the simplest alkyne, with organomagnesiums can result either in mono or dimetallation. Dimetallation is achieved, e.g., by passing acetylene through ethylmagnesium bromide in Et20 ... 

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