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Topic: Thoughts on this mechanism?  (Read 2536 times)

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Offline trinitrotoluene

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Thoughts on this mechanism?
« on: August 31, 2013, 03:21:47 PM »
Hey Guys, I am trying to propose a reasonable mechanism for this transformation. I gave my best go at it, but it seems a little shady. Just wondering if this seems plausible or if there any other suggestions on how to go about the transformation.

Thanks!


Offline spirochete

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Re: Thoughts on this mechanism?
« Reply #1 on: September 02, 2013, 09:39:54 PM »
You've drawn a couple of elimination steps as concerted that I would expect to be stepwise. Protons alpha to a carbonyl group are relatively acidic, so you can make an enolate first, then expel the leaving group to form a pi bond. This is called E1cb (E1 conjugate base). 

Offline spirochete

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Re: Thoughts on this mechanism?
« Reply #2 on: September 02, 2013, 09:44:25 PM »
Also you magically made the phenolic hydroxyl group dissapear in the last step.

Offline orgopete

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Re: Thoughts on this mechanism?
« Reply #3 on: September 02, 2013, 10:27:24 PM »
I had to work through this backwards to understand it. None the less, I am concerned that only one product formed. With the proposed mechanism, the cyclopropane cold open two ways to give similar products. This is what I think happens. It does no decarboxylation initially, but now the most acidic proton is that alpha to the benzo group. Open the cyclopropane to give the enolate of a beta keto-acid. You can rationalize a path for the remainder of the steps.
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Offline trinitrotoluene

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Re: Thoughts on this mechanism?
« Reply #4 on: September 03, 2013, 05:55:15 PM »
You've drawn a couple of elimination steps as concerted that I would expect to be stepwise. Protons alpha to a carbonyl group are relatively acidic, so you can make an enolate first, then expel the leaving group to form a pi bond. This is called E1cb (E1 conjugate base).
Also you magically made the phenolic hydroxyl group dissapear in the last step.

Thank you for the input ^_^ I suppose I should be more careful with concerted vs. stepwise. I have always been bad with that. Also, I don't know why I forgot the phenol, but it should be there.

I had to work through this backwards to understand it. None the less, I am concerned that only one product formed. With the proposed mechanism, the cyclopropane cold open two ways to give similar products. This is what I think happens. It does no decarboxylation initially, but now the most acidic proton is that alpha to the benzo group. Open the cyclopropane to give the enolate of a beta keto-acid. You can rationalize a path for the remainder of the steps.

We were given the reaction and just propose a mechanism. At first I did open the the ring differently, and got to another product. I will work out your suggestions though and see how it turns out differently

Thank you! ^_^

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