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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: Rakkoonn on May 31, 2007, 03:02:44 AM

Title: Knoevenagel Condensation mechanism (coumarin dereviative synthesis)
Post by: Rakkoonn on May 31, 2007, 03:02:44 AM

I'm trying to figure out the mechanism of the following reaction:

(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fi38.photobucket.com%2Falbums%2Fe129%2FSowaSowa%2Fcoum01.gif&hash=c1b4d4951f0399c6a0a54b39adf23ecfcce814c6)

I was told that it's a Knoevenagel condensation in the first step and then a cyclisation occurs. If I apply this scheme to my reaction it will look like this:

(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fwww.organic-chemistry.org%2Fnamedreactions%2Fknoeve3.gif&hash=d8ea8f7afa6da12ec1b3706746ac3a13f9ea4af1)

(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fi38.photobucket.com%2Falbums%2Fe129%2FSowaSowa%2Fcoum02.gif&hash=796364e447d3989818563af927b30ac00c562620)


It doesn't look right. How does the cyclisation go?

Title: Re: Knoevenagel Condensation mechanism (coumarin dereviative synthesis)
Post by: Dolphinsiu on May 31, 2007, 06:11:52 AM

It is not Knoevenagel condensation, it is just simply an aldol condensation.

     O                O         O                      O         O
     ll                 ll          ll                       ll          ll
R - C - H + HO - C - C - C - OH --->  HO - C - C - C - OH
                                                                ll
                                                                C - R

Then cyclisation(intra-esterification) follows and the product is resulted.

Title: Re: Knoevenagel Condensation mechanism (coumarin dereviative synthesis)
Post by: AWK on May 31, 2007, 07:34:05 AM

http://www.organic-chemistry.org/namedreactions/knoevenagel-condensation.shtm

Malonic acid easily decarboxylate, use its ester

Title: Re: Knoevenagel Condensation mechanism (coumarin dereviative synthesis)
Post by: english on May 31, 2007, 02:07:19 PM

I thought Knoevenagel didn't work too well with 3­° amines.  You only need a catalytic amount anyway.

Title: Re: Knoevenagel Condensation mechanism (coumarin dereviative synthesis)
Post by: kiwi on May 31, 2007, 05:45:20 PM

Quote from: Dolphinsiu on May 31, 2007, 06:11:52 AM

It is not Knoevenagel condensation, it is just simply an aldol condensation.

that is a Knoevenagel condensation. And as for post one, what do alcohols and acids do in acidic media?