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Topic: pericyclic reaction question  (Read 2020 times)

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Offline tulip11

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pericyclic reaction question
« on: May 15, 2018, 07:19:57 PM »
I'm trying to do this question pasted below but am quite stuck although I think I understand the subject matter quite well. I thought for pericylcilc electrocyclisations in terms of conrotatory/disrotatory motion there had to be a conjugated pi system which i am then confident reacting using woodward-Hoffmann rules of the FMO approach. However in this system there doesnt seem to be a conjugated pi system. I have considered doing a photo [2+2] cycloaddition of the double bond that doesn't appear to answer the question and also thought about using a cope rearrangment but couldnt get the right product for that! If anyone could point me out along the right direction or give me a hint for the first step that would be great.

Offline Mitch

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Re: pericyclic reaction question
« Reply #1 on: May 16, 2018, 04:05:06 PM »
If the arrow was pointing the other way, would it make more sense?
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Offline tulip11

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Re: pericyclic reaction question
« Reply #2 on: May 16, 2018, 06:21:52 PM »
Oh I think so - would it just be a single disrotatory ring closure? And would you then consider it a 6pi system so be thermally allowed?

Offline pgk

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Re: pericyclic reaction question
« Reply #3 on: May 17, 2018, 11:47:47 AM »
There is no need to be a conjugated π bonds system, in order to a pericyclic reaction occurs. Just double bonds that are close enough and so, their HOMO/LUMO π orbitals can overlap each other. Typical examples are the either thermal or photochemical dimerization of monounsaturated fatty acid and fats.
Question 1: The methyl group and the neighbor proton in the cyclobutane moiety of the obtained product, have a syn- conformation. What does this mean, regarding the conrotatory/disrotatory pericylization?
Question 2: How many π bonds or else, how many double bonds do you see and what does this mean, regarding the thermodynamic/pericyclic process, in relation to conrotatory/disrotatory pericylization?
Hint: https://en.wikipedia.org/wiki/Conrotatory_and_disrotatory
« Last Edit: May 17, 2018, 12:32:37 PM by pgk »

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