[Bakterien]

I wonder if its possible to make the following Grignard reagent: Br-CH2-O-CH3    +       Mg ------>  BrMg-CH2-O-CH3

Will the oxygen mess it up somehow ? Non of the protons are very acidic

If it is possible, could I use it to attack an imine ? In order to form the amine ? 

[rolnor]

You can make bensyloxymethyltributyltin and this can be transmetalated with butyllithium to form bensyloxymethyllithium at -78°C.
I have never seen the methoxymethylmagnesiumbromide you want to make, I think you get alpha-elimination or Wurtz-type coupling if you try to make it from methoxymethylbromide and magnesium. It was some years ago I made this chemistry so I could be remembering things wrong.