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Topic: Iodine addition on alkenes  (Read 7544 times)

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Offline mir

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Iodine addition on alkenes
« on: May 26, 2006, 10:16:17 AM »
I guess I have figured out the upper mechanism.
But the lower reaction is causing me to bite my nails and drinking to much coffee. All in all, I need help. On monday I have an oral exam in physcial org chemistry :-/
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Offline Dan

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Re: Iodine addition on alkenes
« Reply #1 on: May 26, 2006, 11:19:10 AM »
How about this:

1. Form the iodonium ion as normal
2. Decarboxylate to open the 3 mem ring
OR
Open to give the tertiary carbocaton, which is rapidly trapped by the CO2H, forming a 4 membered ring
Reverse [2+2] cycloaddition, eliminating CO2

3. SN2 by water
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Offline Dan

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Re: Iodine addition on alkenes
« Reply #2 on: May 26, 2006, 11:53:26 AM »
Like this http://users.ox.ac.uk/~some1599/Images/mech.jpg

It's a bit scruffy, but I had to use use paint, so...
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Offline movies

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Re: Iodine addition on alkenes
« Reply #3 on: May 26, 2006, 01:17:33 PM »
How about just forming the diiodide, then deacarboxylate and eliminate one of the I's, then SN2 (or SN2') with water to displace the other.
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Offline Dan

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Re: Iodine addition on alkenes
« Reply #4 on: May 26, 2006, 02:19:08 PM »
Yeah that seems more likely, seeing as KI about, good call.
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Offline mir

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Re: Iodine addition on alkenes
« Reply #5 on: May 26, 2006, 04:58:38 PM »
Quote from: movies on May 26, 2006, 01:17:33 PM
How about just forming the diiodide, then deacarboxylate and eliminate one of the I's, then SN2 (or SN2') with water to displace the other.

Like this?

I wasnt sure about the decarboxylation step.
I understand now. In such problems, you have to dare to use the imagination.
Even if you have to form a sterically extreme cyclobutane-like ring.
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No single thing abides, but all things flow.
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Until we know and name them.
Then by degrees they change and are no more
The things we know.
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Offline movies

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Re: Iodine addition on alkenes
« Reply #6 on: May 28, 2006, 06:51:52 PM »
Not quite, I was thinking that the second compound you have drawn there would decarboxylate with the electrons from the C-C bond that you would break kicking down to diplace the adjacent I and from the C=C double bond.
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