Would you care to make a prediction and explain your reasoning?
After first cyclopentadiene allylic bromination I have:
- one allylic position with an Hydrogen and a bromine
- the other allylic position with two hydrogen
Now the second NBS equivalent could react with the allylic position already brominated or with the pther one
Now looking at the mechanism I get a radical when the C-H bond is cleaved by Br·
Now I don't know if I can say that a radical carbon is an electrophilic carbon and an halogen near it will destabilized that.
So the bromination will occour on the other allylic position where I don't have any halide
Another explanation is the steric hindrance
Br has a big steric hindrance and is hard for the second Br· to attack the allylic postion where is already bonded a Br
But I don't know if these explanations are good