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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: zsinger on July 19, 2014, 09:47:16 AM

Title: Help with a synth.
Post by: zsinger on July 19, 2014, 09:47:16 AM

All,
I was helping an undergraduate student, and I ran into a synthesis which I just could not figure out for some reason.  Maybe I am having a brain fart, but see what y'all think.  The ONLY idea I had was starting with trans-2-phenyl-1-cyclohexanol, modifying it perhaps, and doing some sort of EAS.  Im sorry for the lack of a pic, so I will attempt to name it and describe it best I can, and maybe one of the nice mods will draw it for me.  I read the formatting and have no idea how to draw this one still:

I believe the name would be 1-Phenyl-Cyclohexene (phenyl ring attached to a cyclohexene -->The Phenyl ring is attached directly to one of the carbons participating in the double bond)

Any help appreciated.
         -Zack

Title: Re: Help with a synth.
Post by: zsinger on July 19, 2014, 09:52:59 AM

Could one simply add sulfuric acid to cyclohexanol WITHOUT heat (Perhaps very low temp) to create a stable CC that will react with benzene?  I have never tried this, but it sounds like it might work?  The low temps would keep the HSO₄^- from snagging the proton, forming the alkene presumably.
         Zack

Title: Re: Help with a synth.
Post by: Dan on July 19, 2014, 10:09:08 AM

So the target is:



Any restrictions as to starting materials?

zsinger - benzene is a very poor Friedel-Crafts nucleophile. You could do something like that with anisole etc. But benzene will not work well. Then you have the classic overalkylation issue as well. The product would need further manipulation to install the alkene.

The target screams "cross coupling" to me!

Title: Re: Help with a synth.
Post by: zsinger on July 19, 2014, 10:47:54 AM

I screamed cross coupling as well, but it is NOT taught in their curriculum.  Weird.  Benzene was the required starting material.
              -Zack

Title: Re: Help with a synth.
Post by: zsinger on July 19, 2014, 10:57:09 AM

I found a writeup which first makes the CC from cyclohexene, reacts it with benzene in an EAS, followed by a benzyllic bromination, then dehydrohalogenates forming the double bond.  Any takers?
                -Zack

Title: Re: Help with a synth.
Post by: discodermolide on July 19, 2014, 12:43:07 PM

Seems a bit silly to start with a C=C, remove it and then re-make it!

Title: Re: Help with a synth.
Post by: zsinger on July 20, 2014, 02:26:25 PM

Cross coupling seems most likely, after consulting with several professors.

Title: Re: Help with a synth.
Post by: orgopete on July 21, 2014, 07:09:16 AM

It looks Grignardy to me.

Title: Re: Help with a synth.
Post by: zsinger on July 21, 2014, 11:38:30 AM

Orgo…..What would be the electrophilic synthon be?
         -Zack

Title: Re: Help with a synth.
Post by: orgopete on July 21, 2014, 11:54:25 AM

Cyclohexanone

Title: Re: Help with a synth.
Post by: zsinger on July 22, 2014, 12:56:54 PM

So make the alcohol, then dehydrate as per usual E1 with H2SO4 and Δ?
                -Zack

Title: Re: Help with a synth.
Post by: orgopete on July 22, 2014, 03:03:14 PM

Quote from: zsinger on July 22, 2014, 12:56:54 PM

So make the alcohol, then dehydrate as per usual E1 with H2SO4 and Δ?
                -Zack

That is what I would think. That route seems simple and very much like the chemistry of an intro ochem course. Obviously if the problem restricts you to five carbons or less, it may be different. If it is a problem in a chapter of Grignards, then definitely.

Title: Re: Help with a synth.
Post by: zsinger on July 23, 2014, 06:04:36 PM

Perhaps forming the incipient CC is best achieved by reaction with a Lewis Acid?