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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: Tiger on November 11, 2004, 01:06:22 AM

Title: Pechmann Condensation mechanism
Post by: Tiger on November 11, 2004, 01:06:22 AM

Please help me with the second part of the mechanism. I got the first part but I'm not sure how to get to the product.

Here is the link to the reaction

http://themerckindex.cambridgesoft.com/TheMerckIndex/NameReactions/ONR295.htm

Thanks

JN

Title: Re:Pechmann Condensation mechanism
Post by: Tiger on November 11, 2004, 02:21:38 AM

How can I obtain this article?

H. v. Pechmann, C. Duisberg, Ber. 16, 2119 (1883)

Title: Re:Pechmann Condensation mechanism
Post by: Mitch on November 11, 2004, 02:18:06 PM

It's in german.

Title: Re:Pechmann Condensation mechanism
Post by: movies on November 11, 2004, 04:37:41 PM

So I assume you got through the trans-esterification part.

The next step is formation of the enol tautomer of the beta-keto ester.  From there the Lewis acid can activate the remaining carbonyl group to do a Michael addition to form the second ring.  Then you just eliminate water to form the enone.

Title: Re:Pechmann Condensation mechanism
Post by: Tiger on November 12, 2004, 01:19:21 AM

Thanks to Mitch and Movies.

I went to the library and found that article. The book was so so so so old and smelly. It's in German. I had someone translate the article for me.

JN

Title: Re:Pechmann Condensation mechanism
Post by: AWK on November 12, 2004, 02:06:49 AM

In this reference you will not find any information on mechanism. This is
multiple-transformation process which involves hydroxyalkylation at 2-position of substituted phenol, transesterification and dehydration

Title: Re:Pechmann Condensation mechanism
Post by: pumpkins on November 12, 2004, 10:36:52 AM

probably it goes like this:

Title: Re:Pechmann Condensation mechanism
Post by: Mitch on November 12, 2004, 02:25:41 PM

Thanks Pumpkins.

Nothing smells better than an old German book. :P

Title: Re:Pechmann Condensation mechanism
Post by: Tiger on November 13, 2004, 12:07:20 AM

Quote from: Mitch on November 12, 2004, 02:25:41 PM

Thanks Pumpkins.

Nothing smells better than an old German book. :P

Yup, it's very smelly. I finished my paper last night and turned in today. I have to do a presentation on Pechmann condensation. I haven't done this type of presentation before. Any suggestion??? My prof said that he didn't like Power Point or anything.. use chalk and board...

Title: Re:Pechmann Condensation mechanism
Post by: movies on November 14, 2004, 12:41:01 PM

I would start by showing the general transformation for the condensation, then talk about the proposed mechanism.  If you could find some examples of the reactions use in synthesis, that would be a nice addition as well.  You could show where the Pechmann was used in the synthesis and then how that maps onto the final target molecule.  There are a lot of natural products that contain coumarin rings.

Title: Re:Pechmann Condensation mechanism
Post by: Tiger on November 23, 2004, 03:01:58 AM

My prof just gave me back my research paper. Oh my goodness, after I took the paper from his hands I hardly saw any black ink on the paper, all red ink  :-[ :'(