I am having a problem about bromination reaction.Attached please find the reation. I tried many conditions but all of them give a mixture of di-bromide, mono-bromide and ary-bromide. Moreover, the starting material was remaining. Considering the side prodcuts would generate, NBS,Br2 or CuBr2 was only used with 1-1.5 eq. Many solvents are also screeened, such as HOAc,CHCl3,CHCl4,DMF,MeOH,diethyl ether,even the mixed solvents.But gave messy TLC and low yield.As a result, I tried to treat the starting material with TMSCl and then bromize it with NBS or CuBr2, but it still gave a mixture of mono-bromide and di-bromide.
All the procedure and result drive me crazy!Anyone is experienced in this class of reaction?Any suggestion will be appreciated.