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Topic: complete cleavage of carbonyl groups anyone?  (Read 4436 times)

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Offline theufomusic

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complete cleavage of carbonyl groups anyone?
« on: December 24, 2006, 04:41:12 PM »
Hello, Im just an Ex chemistry student (I completed second year, but didn't pass) and
im now wondering (just a thought experiment) if there is a way to completely cleave off
a carbonyl group and its carbonyl carbon; i.e Alpha cleavage (if I remember correctly.)

also, what would be a suitable reagent for performing this with an aromatic carbonyl?
Thankyou!

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Re: complete cleavage of carbonyl groups anyone?
« Reply #1 on: December 24, 2006, 05:11:45 PM »
You can sometimes decarbonylate aldehydes with Rhodium(I) catalysts.  Ketones are much more difficult.  You could consider Baeyer-Villiger oxidation followed by hydrolysis.

Offline nottingham

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Re: complete cleavage of carbonyl groups anyone?
« Reply #2 on: December 24, 2006, 05:30:50 PM »
You can sometimes decarbonylate aldehydes with Rhodium(I) catalysts.  Ketones are much more difficult.  You could consider Baeyer-Villiger oxidation followed by hydrolysis.

good idea.

Offline theufomusic

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Re: complete cleavage of carbonyl groups anyone?
« Reply #3 on: December 26, 2006, 12:28:41 AM »
Thanks! that might work.

Offline Custos

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Re: complete cleavage of carbonyl groups anyone?
« Reply #4 on: January 14, 2007, 09:04:33 PM »
You can sometimes decarbonylate aldehydes with Rhodium(I) catalysts.  Ketones are much more difficult.  You could consider Baeyer-Villiger oxidation followed by hydrolysis.
If you did a Baeyer-Villiger oxidation followed by hydrolysis on an aromatic ketone wouldn't you end up with the corresponding phenol? ... depending of course what was on the other side of the ketone - if the migratory ability of the other substituent was better than aryl you would end up with the arylcarboxylic acid which might decarboxylate. It's not really a decarbonylation though is it? Straight decarbononylation can be tough and it would depend on the specific example.

Offline theufomusic

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Re: complete cleavage of carbonyl groups anyone?
« Reply #5 on: January 14, 2007, 09:15:26 PM »
Its tryptophan, actually ...

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Re: complete cleavage of carbonyl groups anyone?
« Reply #6 on: January 15, 2007, 12:54:55 PM »
You can sometimes decarbonylate aldehydes with Rhodium(I) catalysts.  Ketones are much more difficult.  You could consider Baeyer-Villiger oxidation followed by hydrolysis.
If you did a Baeyer-Villiger oxidation followed by hydrolysis on an aromatic ketone wouldn't you end up with the corresponding phenol? ... depending of course what was on the other side of the ketone - if the migratory ability of the other substituent was better than aryl you would end up with the arylcarboxylic acid which might decarboxylate. It's not really a decarbonylation though is it? Straight decarbononylation can be tough and it would depend on the specific example.

Yes, you're absolutely right.  I was trying to come up with ways to cleave the C-C bond, which I think is the hardest part.  You would end up with an alcohol, and your options for reducing an alcohol to an alkane are a lot better (TsCl then LAH, Barton-McCombie deoxygenation, etc.).

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