[mir]

Reaction conditions: Fuming bromic acid, HBr

(+/-)-2,3-dibacetoxybutane --> [ (+/-)-erythro-3-bromo-2-butanol]
--> meso-2,3-dibromobutane

(+/-)-erythro-3-bromo-2-butanol is an intermediate in the reaction.

How can I account for the stereochemistry of the product, when the reactants are a racemic?
I think there is an epoxide formed somewhere.

Thank for all your answers :-)

[mir]

(+/-)-2,3-dibacetoxybutane

I meant of course (+/-)-2,3-diacetoxy-butane (with no letter "b")

Is this exercise so hard? I havent made it yet... But I still working. Anyone, who can give a hint?

[movies]

Can you remind us of how threo and erythro work?  I can never remember.

Is the attached picture a correct description?

[mir]

Maybe I should I have done this already in the beginning of the thread.
But here are what I have figured out until know. Still there is a mystery about the first step.
I cant figure out why the erythro-compund of the halohydrin is formed.

Thanks for the answers so far :-)

[movies]

I think you have the second part right with the epoxide formation.  The first part is definitely tricky though.

Here's a hint: the first step is to protonate one of the acetates.  What nucleophiles are around to react with this now?  What would be the relative stereochemical outcome of the reaction with these nucleophiles?