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Offline xile1990

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quesnoin
« on: January 27, 2008, 01:43:04 AM »
in j. org. chem. 2008, 73, 412-417...

the mechanism in scheme 1 looks wrong.  i am trying to think of an alternative mechanism.  any ideas?

Offline Yggdrasil

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Re: quesnoin
« Reply #1 on: January 27, 2008, 12:09:04 PM »
http://dx.doi.org/10.1021/jo701544k

Here's a link to the article for those with a subscription.

Offline agrobert

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Re: quesnoin
« Reply #2 on: January 27, 2008, 07:37:53 PM »
I agree.  It is funny becuase I was directed to this article form C&EN and before reading it I had proposed a retrosynthesis starting from the acid end of the diterpene.  Glad to see someone else interested in this unique molecule.  If you start from the acid retrosynthetically you can break the rings open to form the typical terpene 5 carbon units with the methyl after every third carbon.  Although in nature I believe the more complicated ring containing the transannular ether would be synthesized last because it is probably the least stable.  They propose a radical mechanism and those are always skeptical because radical intermediates are difficult to trap.  Perhaps a proposed total synthesis or reference to a similar molecule would be helpful.  The first ste pin the scheme looks okay but they cut out steps of stabilized carbocations for simplicity. 
In the realm of scientific observation, luck is only granted to those who are prepared. -Louis Pasteur

Offline Shaun

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Re: quesnoin
« Reply #3 on: February 08, 2008, 02:20:13 PM »
They left out some details.  The way the reaction is drawn would be impossible but the mechanism is correct if you go through each step thoroughly.

In the last step, the O radical abstracts an H radical from the carbon atom which will end up bonded to the O.  Carbon radicals are more stable than O radicals.

Next, a peroxide radical abstracts an H radical from the OH.  We now have an O radical that can form a single bond with the C radical.

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