[Rutherford]

One nitrogen in the nitrogen molecule would have 2- charge.

[discodermolide]

you got the structure, you figure out the charges pls

[Rutherford]

In the path you wrote. the nitrogen doesn't lose it's negative charge, so in the formed nitrogen molecule one nitrogen would be negative.

[discodermolide]

Then in the drawing I forgot to change it.

[orgopete]

I didn't know this right off, so I had to do some searching for some of the steps. I suggest you write out every single step. Then it might be helpful to draw the alternate form of the azide. I think the cyclization step may look different and the radical mediator mechanism will change. I don't think there is any Me3SiH forming.

[discodermolide]

Thanks orgopete,
How do you see this proceeding?. There is a Google books reference to domino reactions, this is in there.
sorry for the long link
http://books.google.ch/books?id=HfdEud1Qvq0C&pg=PA229&lpg=PA229&dq=horsfiline+synthesis&source=bl&ots=7PPPMvUUwd&sig=VRI_o85y_Wm4GbOC1bXi5JE-p6c&hl=en&sa=X&ei=EtsJU-2mIOL_ygO33oHACw&ved=0CFwQ6AEwCjgK#v=onepage&q=horsfiline%20synthesis&f=false

I invoked the R₃SiH to provide a source of the H radical after (during) the nitrogen elimination. So you end up with a radical initiator for the next reaction.

[Rutherford]

I got this:

[discodermolide]

That's OK, but where does the H radical come from?

[Rutherford]

They gave above the reaction arrow: +H⁺ and -N₂, although I think that it is a mistake and that it should be radical hydrogen.

[discodermolide]

I think it comes from the silane.
Let's see if orgopete has a different source.

[orgopete]

In the scheme, it was written as "+H⁺". Since the literature was using TTMSS, it showed a TMS on the nitrogen. This propagated the radical for cleaving the iodine and initiating the reaction. So I presume protonation was to cleave the silyl group. I didn't see any other hydrogen source. If a tin hydride were used, that would be different.