Synthesis of trans alkene with organoborane Trans alkenes can be synthesized with organoboranes. The following sequence is represented in Smith's Organic Synthesis


How does the mechanism look like after the first step (hydroboration)?
I think this might be a alkyl shift that results in an $\mathrm{S}_{N}2$ type substitution at an $sp^{2}$ center. Cool. I've only ever seen $\mathrm{S}_{N}2$ type substitution at an $sp^{2}$ center for vinyl iodides. Unfortunately, I don't have my teaching materials on me at work, so I can't find the reference for this for you.

EDIT:


Note the "inversion" at the $sp^{2}$ center.

Greg Fu had this great example of a substitution on a vinyl iodide, like I mentioned above. I can't seem to find this reference, but I just emailed him, so I'll update when he writes me back.