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).