# How can I have a concerted addition of bromines?

I know how to add Bromines in the antiperiplanar position, but I have no idea how to get concerted addition:

Perhaps I am not seeing something obvious, but I would greatly appreciate any hint.

• As briefly mentioned in the answer, concerted does not mean what you think it means. It means that a reaction proceeds in one step, without any intermediates. Examples of concerted reactions are the $\mathrm{S_N2}$ reaction, or the Diels-Alder reaction - see Wikipedia. – orthocresol Dec 15 '15 at 0:03

The proper term for concerted addition is syn addition. I can't find any way of a direct way of producing a syn-addition product. The only way I can figure you would have to do it is if you did the halogenation with water as the solvent you would get the halo-hydrin product with an anti-addition. You could then follow this up with a bromination using $\ce{P,Br2}$ or $\ce{PBr3}$ which would invert the chirality and give you a syn-product.