Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: AlphaScent on July 07, 2015, 03:34:39 PM
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I was shown a compound and asked how one may synthesize it. I finally put my thoughts down on paper.
I have a reference for the first two steps. The starting material is very cheap. That is why I started with it.
My questions are the validity of the Birch reduction and the subsequent step. Is ipso going to predominate for the esters? Should I worry about Birch alkylation? Elimination? Transmetallation?
I know the hydrolysis and tautomerization are sound but will elimination predominate? I am worries about hydride shifts to give the double bond in the ring.
The symmetry of the molecule helps with the Rubottom oxidation. The bromination conditions may not be the best because of sterics.
Please let me know your thoughts.
cheers!!
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not letting me load my chemdraw. Give me a bit
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Here it is.
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There are a number of problems here:
1. The esters (OAc) are unlikely to survive treatment with ammonia
2. The bromomethyl group is unlikely to survive Birch reduction
3. In the presence of base, the double bond in in 5-methylenecyclohexa-1,3-diene would probably isomerize into conjugation with one of the ketones - the resulting enone will then tautomerise to 3-hydroxy-5-methylphenol (your original starting material)
4. The double bond in in 5-methylenecyclohexa-1,3-diene might react with mCPBA (though more slowly than with the enol ether)
5. The double bond in in 5-methylenecyclohexa-1,3-diene would probably react with bromine
The recurring problem is that the reagents you are choosing are not chemoselective enough for your proposed intermediates.
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To elaborate on what dan said about the Br. I think you gotta make the α-tolyl position into a bad leaving group like ROH, and before the birch reduction is the best time to do this because no E2/E1; it will become deprotonated during the birch reduction and make into a horrible leaving group. SN1 will happen with the NH2+RCH2Br. Will still get elimination product because of pKa RNH2>NH3 the anion will sit next to a LG and elimination will happen which I think will lead to a hydride shift to some extent (how much not sure).
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Thank you so much. Some very trivial mistakes on my part. A bit hasty. The esters would go through ammoniolysis and the bromide would not survive. The base catalyzed isomerization (tautomerization) to the starting material is quite clear now. I will go back to the drawing board and come up with something more chemoselective.
Cheers!
Thanks for the critique, much appreciated!!