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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: Rutherford on February 16, 2013, 08:03:17 AM

Title: Chrysanthemic acid scheme
Post by: Rutherford on February 16, 2013, 08:03:17 AM
This scheme has to be done in reversed order, that's why it gives my a headache.
(http://img571.imageshack.us/img571/2660/scheme1x.gif)
Hint: A is a gaseous hydrocarbon with the density lower than that of air.

A is probably either C2H2 or C2H4. In the B reaction scheme, it gives a positive result to the iodoform reaction, so I is probably a methyl secondary alcohol, produced by acidification of B which is an alcoxide.
What reaction of A and B happens at the specified conditions?
Title: Re: Chrysanthemic acid scheme
Post by: discodermolide on February 16, 2013, 08:10:37 AM
So F is an ester. N is a tosylate, H a bromide, M an alkene, L an acetylene, start with that.
Title: Re: Chrysanthemic acid scheme
Post by: Rutherford on February 16, 2013, 08:35:14 AM
I understand all that, but I need the first reaction. Don't know how to determine anything without it.

Till now, I know that:
-F is an ester (know the structure), N is a tosylate, H a bromide, M an alkene, L an alkyne.
-K is an ester, J an acid salt, I a methyl secondary alcohol, B an alkoxide.
Title: Re: Chrysanthemic acid scheme
Post by: Rutherford on February 16, 2013, 08:51:04 AM
I am not sure if the molecular formula for N is correct. The chrysanthemic acid has 10 C atoms, while N has 12, so F will have at least 12, too  ???.
Title: Re: Chrysanthemic acid scheme
Post by: discodermolide on February 16, 2013, 10:27:41 AM
Once again you are not presenting the full information!
Have you read the PDF you posted in the Chem Education forum? If so you would have read that the first reaction was discovered by Favorskii in 1905 http://en.wikipedia.org/wiki/Favorskii_reaction (http://en.wikipedia.org/wiki/Favorskii_reaction)
This is probably your first step.
I also note they present 2 routes to this compound. See if you can work it out now.
Title: Re: Chrysanthemic acid scheme
Post by: Rutherford on February 16, 2013, 10:59:39 AM
Sorry for that. I thought that it is more informative than needed to know and I thought first to do one scheme and then the other one. I will try to solve it now when knowing the reaction.
Title: Re: Chrysanthemic acid scheme
Post by: discodermolide on February 16, 2013, 11:18:25 AM
Compound E is probably this one.
C/C(C)=C/C=C(C)/C
Title: Re: Chrysanthemic acid scheme
Post by: Rutherford on February 16, 2013, 11:33:13 AM
Yes, I finished the first scheme, now I am back to the second one. Why is the acid added to B (which I got that is acetone)?
Title: Re: Chrysanthemic acid scheme
Post by: discodermolide on February 16, 2013, 11:54:51 AM
What did you get for A+B :rarrow:L ?
Title: Re: Chrysanthemic acid scheme
Post by: Rutherford on February 16, 2013, 12:40:17 PM
Attached. Now I think HBr won't be added according to Markovnikof's rule. As N contains only 2 O atoms, what happened to the -OH group? Was it eliminated with HBr?
Title: Re: Chrysanthemic acid scheme
Post by: discodermolide on February 16, 2013, 12:47:50 PM
I think this is H
C/C(C)=C/CBr
Title: Re: Chrysanthemic acid scheme
Post by: Rutherford on February 16, 2013, 12:55:46 PM
And then the tosilate is introduced. To finish the scheme I need K. I assumed that L is made from acid catalyzed aldol addition of acetone. I finished up with K being the attached compound. Could that be K? If yes, what happens then in reaction with the tosilate and NaOMe?
Title: Re: Chrysanthemic acid scheme
Post by: discodermolide on February 16, 2013, 01:07:28 PM
I think this is N:
C/C(C)=C/CS(C1=CC=C(C)C=C1)(=O)=O

It's not a tosylate but a sulfone.
Please show me your scheme B :rarrow: I :rarrow: J :rarrow: K
Title: Re: Chrysanthemic acid scheme
Post by: Rutherford on February 16, 2013, 01:18:56 PM
Here it is. Is it ok? If yes, what happens with K and N afterwards?

Didn't write that A is acetylene.
Title: Re: Chrysanthemic acid scheme
Post by: discodermolide on February 16, 2013, 01:22:59 PM
OK, now what happens to give F?
Title: Re: Chrysanthemic acid scheme
Post by: Rutherford on February 16, 2013, 01:38:34 PM
That's what bothers me. I can't think of the reaction  :-\.
Title: Re: Chrysanthemic acid scheme
Post by: discodermolide on February 16, 2013, 01:48:56 PM
Yes, I didn't think you would get it. OK, the sulfone makes the CH2 group next to it quite acidic, so you can generate a carbanion which attacks what? In a named reaction. I must say that I think the yield of this may be quite low. Also note you have the ethyl ester and are using methoxide as a base so it will transesterify to give product F as the methyl ester. If you can't figure it out I'll post my scheme of what I think goes on.
Title: Re: Chrysanthemic acid scheme
Post by: Rutherford on February 16, 2013, 02:17:54 PM
I don't see a way to combine those three compounds  ???.
Title: Re: Chrysanthemic acid scheme
Post by: discodermolide on February 16, 2013, 02:22:22 PM
Two compounds. As I said the base abstracts a proton from the CH2 of the sulfone, this adds in  michael reaction to the ester K, the intermediate enolate attacks the carbon carrying the sulfone forming the three membered ring and eliminating the sulfone. Have a look at my scheme.
Title: Re: Chrysanthemic acid scheme
Post by: Rutherford on February 16, 2013, 02:24:27 PM
Shouldn't an ethyl ester be obtained?
Title: Re: Chrysanthemic acid scheme
Post by: discodermolide on February 16, 2013, 02:27:24 PM
Using NaOMe, I would expect transesterification, if they use methanol as a solvent, if not then the ethyl ester remains.
It doesn't matter as it is hydrolysed anyway.

Title: Re: Chrysanthemic acid scheme
Post by: Rutherford on February 16, 2013, 02:33:19 PM
Yes, but structure of F is important, too. As it appears in the previous scheme, where I got that it is an ethyl ester, it has to be the same here. Didn't think of this earlier  ::).
Thanks for the help.
Title: Re: Chrysanthemic acid scheme
Post by: discodermolide on February 16, 2013, 02:36:33 PM
No problem.
Then they must have used NaOMe in a solvent like THF or toluene. Then the ethyl ester remains an ethyl ester.
p.s. I have actually made some of these compounds, although not by this methodology. But I can't disclose their structures.
Title: Re: Chrysanthemic acid scheme
Post by: Rutherford on February 17, 2013, 06:24:30 AM
Got one issue now. In the attached scheme, G is a natural alcohol. H is the same compound that was present in the previous scheme. What is G then? I have a formula, but I don't recognize this alcohol.
H is:
CC(C)=CCBr
I got that G is:
CC(C)=CCO
Is this a natural alcohol?
Title: Re: Chrysanthemic acid scheme
Post by: discodermolide on February 17, 2013, 07:59:18 AM
Yes, it is
http://en.wikipedia.org/wiki/Prenol (http://en.wikipedia.org/wiki/Prenol)
Title: Re: Chrysanthemic acid scheme
Post by: Rutherford on February 17, 2013, 08:11:13 AM
Huh, thanks. It would be a mess if it wasn't.
Title: Re: Chrysanthemic acid scheme
Post by: Rutherford on February 17, 2013, 10:32:34 AM
How to draw the (1R,3R)-configuration of chrysanthemic acid? I don't know how to apply the Cahn-Ingold system here. How to do it? I think that the stereocenters are in the ring.
Title: Re: Chrysanthemic acid scheme
Post by: sjb on February 17, 2013, 10:34:56 AM
How to draw the (1R,3R)-configuration of chrysanthemic acid? I don't know how to apply the Cahn-Ingold system here. How to do it? I think that the stereocenters are in the ring.

There's no difference to if it were not in a ring. Which two atoms are the stereocentres?
Title: Re: Chrysanthemic acid scheme
Post by: Rutherford on February 17, 2013, 10:39:48 AM
I think that the marked atoms are the stereocenters. Which one is 1R and which one is 3R? How to apply the Cahn-Ingold system?
Title: Re: Chrysanthemic acid scheme
Post by: discodermolide on February 17, 2013, 10:53:56 AM
like this?
C/C(C)=C/[C@@]1([H])C(C)(C)[C@]1([H])C(O)=O

(1R,3R)-2,2-dimethyl-3-(2-methylprop-1-en-1-yl)cyclopropanecarboxylic acid

This should be easy for you, we've done enough of them in the past.
Title: Re: Chrysanthemic acid scheme
Post by: Rutherford on February 17, 2013, 11:19:31 AM
I should've known that 1 is the one closer to the -COOH group.
My try is attached. I marked the priorities with numbers. On the top left, I assigned the configuration for the 3 chiral atom, and on the right, I assigned the configuration of the 1 chiral atom. The final structure is on the bottom. Did I do it correct?
Title: Re: Chrysanthemic acid scheme
Post by: discodermolide on February 17, 2013, 11:28:44 AM
Well that compares with the one I posted, so it looks OK :o