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Topic: Organic 1 Synthesis Problems  (Read 31920 times)

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Offline rcrandall

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Re: Organic 1 Synthesis Problems
« Reply #45 on: December 07, 2014, 02:52:01 PM »
Is there another, more stable way that you can think of doing this synthesis? Or should I just stick with what I had?
(Also, thank you. Your explanation of boron makes a lot of sense.)

Offline rcrandall

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Re: Organic 1 Synthesis Problems
« Reply #46 on: December 07, 2014, 03:13:53 PM »
I have "answers" to the other synthesis problems, but I would love it if someone could look them over and correct me on anything I did wrong.
Problem 4
(Is there a difference between using the two different Mercury reactions? Which would be best used?)

Problem 6

Problem 7

Offline Altered State

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Re: Organic 1 Synthesis Problems
« Reply #47 on: December 07, 2014, 03:48:52 PM »
I don't believe there is a better way you can do that problem (5, and the same goes for 6's first step) given your class content.

Problem 4:
First step is OK, but oxymercuriation reaction yields the markovnikov product, and you need the markovnikov. I'd rather go for boron once again.
In regard to the two different Hg reactions, sulphuric acid is just playing a role as a catalyist, and in some cases reaction will work better if you include it, and in some cases it will not. I don't know to what extent adding sulphuric acid is mandatory in this reaction, I'm sorry.

Problem 6:
First step OK.
But you can't perform the hydroboration directly on the haloalkane.
First you need to eliminate the bromine, obtain a double bond, and then get your antimarkovnikov alcohol product.

Problem 7:
First part is OK (although the first two steps can really be just one, heat the starting material with H2O/H2SO4 and you will obtain your third structure)
But that route is not very nice, since in your last step, you cannot selectively oxidize one of the alcohols leaving the other one nonoxidized.

You should find a different path, in which the oxidation step only takes place in one functional group of the molecule (i.e. the other -OH has not been introduced yet)

Hint: Be careful with the second step of the alcohol formation by oxymercuriation reaction, NaBH4 also reduces ketones to alcohols

Offline rcrandall

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Re: Organic 1 Synthesis Problems
« Reply #48 on: December 07, 2014, 04:11:03 PM »
I may be grasping at straws here, but does this work for problem 7?


Offline Altered State

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Re: Organic 1 Synthesis Problems
« Reply #49 on: December 07, 2014, 06:08:01 PM »
The step where you brominate the alpha possition to the cabronyl, its completely doable, but if you have not covered alpha-to-carbonyl reactivity, its probably not the way to go. In case you did cover it, you need first to use a base like LDA, and then Br2.
Also, to do the last step (substitute a bromine for a -OH), you dont need to create a double bond, you can just substitute it with water/acid media.

I would start from a radical bromination on the allylic position

Offline rcrandall

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Re: Organic 1 Synthesis Problems
« Reply #50 on: December 07, 2014, 09:04:30 PM »
Could I use Br2 with peroxide to add the Br to the tertiary carbon, then react with NaOH to replace the Br with an OH?

Offline Altered State

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Re: Organic 1 Synthesis Problems
« Reply #51 on: December 07, 2014, 09:16:22 PM »
Could I use Br2 with peroxide to add the Br to the tertiary carbon, then react with NaOH to replace the Br with an OH?

This is the way to brominate a alpha to cabronyl position http://www.askthenerd.com/ocol/CH22/GIF/A0.GIF (To obtain the enolate required you would need to treat the carbonyk compound with TMSCl, for example)

But in your case, you should not go that way, because is out of your covered content.
I'm suggesting a different route. Some more hints about it:

Start introducing a bromine on the allylic position, something like this, but using NBS instead of Br2 if you've been already taught that reagent: http://jamesash.wpengine.netdna-cdn.com/wp-content/uploads/2013/11/5-allylic.png
Then you can substitute bromine for an -OH using diluted NaOH/H2O (or acidic water), and oxidize it with PCC.
This would leave you with the ketone already on its place, and you just need to figure out how to obtain the alcohol you need from the alkene, without altering the ketone.

Offline rcrandall

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Re: Organic 1 Synthesis Problems
« Reply #52 on: December 07, 2014, 09:32:13 PM »
What steps have I done correctly, and where did I start to go wrong? (Just trying to figure out where to begin with your hints)

Offline rcrandall

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Re: Organic 1 Synthesis Problems
« Reply #53 on: December 07, 2014, 09:44:49 PM »


I had forgotten about NBS, but I found it in my notes.
Will this work?

Offline Altered State

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Re: Organic 1 Synthesis Problems
« Reply #54 on: December 07, 2014, 10:52:38 PM »
Will this work?

Probably not!
I was trying to say that you should treat your starting material directly with NBS under hv conditions.

I'm going to bed now, if you haven't figuered it out by tomorrow since it's for an exam, I'll give you the answer.

Offline rcrandall

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Re: Organic 1 Synthesis Problems
« Reply #55 on: December 07, 2014, 11:10:33 PM »
I was thinking about what I originally had for this problem, and I don't understand what is wrong with it. In that last reaction, the reactant has no reaction with an OH attached to a tertiary carbon. So wouldn't this still give me the product? (I still remember you telling me that I can simplify the first two steps into one)


Offline kriggy

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Re: Organic 1 Synthesis Problems
« Reply #56 on: December 08, 2014, 02:10:15 AM »
I think youre right, after quick search (and little thinking) there is nothing the tertiary alcohol could be oxidized into.
Initialy I was thinking the same as AlteredState but Im pretty sure you can selectively oxidize one of those (well only the secondary since the tertiary has nothing to be oxidized into)

Offline Altered State

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Re: Organic 1 Synthesis Problems
« Reply #57 on: December 08, 2014, 08:43:46 AM »
I think youre right, after quick search (and little thinking) there is nothing the tertiary alcohol could be oxidized into.
Initialy I was thinking the same as AlteredState but Im pretty sure you can selectively oxidize one of those (well only the secondary since the tertiary has nothing to be oxidized into)

Oh yeah, both of you are right, don't know what I was thinking yesterday ???
Of course, PCC will not affect tertiary alcohols. It is all right.

Anyway, be aware that other oxidizers like HIO4 or KMnO4 could break de C-C bond of a diol, giving ketones/carboxylic acids/aldehydes. Even with tertiary alcohols.
But yeah, PCC, will only oxidize your secondary alcohol

Offline Babcock_Hall

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Re: Organic 1 Synthesis Problems
« Reply #58 on: December 08, 2014, 10:12:03 AM »
If your professor wants you to make use of radical halogenation of alkanes, it is probably fine. However, keep in mind that that kind of reaction is highly non-selective, and in real life you will end up with a mixture of polihalogenated compounds in different proportions.
Radical halogenations using bromine should in theory be more selective than those using chlorine.  I hasten to add that I have not performed one myself.
« Last Edit: December 08, 2014, 12:33:23 PM by Babcock_Hall »

Offline rcrandall

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Re: Organic 1 Synthesis Problems
« Reply #59 on: December 08, 2014, 10:59:26 AM »
Well, that's all of the synthesis problems! Thank you all so much for helping me.

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