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Chemistry Forums for Students => Organic Chemistry Forum => Organic Chemistry Forum for Graduate Students and Professionals => Topic started by: dunno260 on November 16, 2009, 03:12:29 AM

Title: Preparation of prenyl magnesium bromide
Post by: dunno260 on November 16, 2009, 03:12:29 AM
I am currently in grignard hell trying to prepare prenyl magnesium bromide from prenyl bromide.  Though I have managed to find two literature procedures for the preparation is preparation has proven to be magnificently difficult.  When I perform the reaction in THF I only get self coupled products and when it is done in diethyl ether I either get no reaction or in a couple of cases self coupled products.

I have tried performing the reaction in either solvent system with fast addition of the prenyl bromide to the solution as well as lengthening the time of addition to 3 hours.  I have tried magnesium turnings straight from the jar with no activation as well as attempts to activate with iodine, 1,2-dibromoethane, and stirring the turnings under argon for 28 hours.  I have also tried magnesium powder that is stored in a glove box using the same procedures as with the magnesium turnings.  I have not yet explored Rieke magnesium though it seems is the next logical step.

I am of course using anhydrous solvents with glassware that is either flame dried immediately prior to use or has sat in our oven for at least 12 hours (160C oven). 
Title: Re: Preparation of prenyl magnesium bromide
Post by: orgopete on November 16, 2009, 09:31:34 AM
I've done it. I used a special apparatus to make the Grignard under high dilution conditions to avoid coupling. I used a mercury activated magnesium. Since that was long ago, I do wonder if it might be done differently. Will a highly activated magnesium work without the coupling?