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Author: Subject: What exactly is the mechanism by which catechols are methylenated? Why does the methylenedioxy group rotate?
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[*] posted on 19-12-2013 at 19:03
What exactly is the mechanism by which catechols are methylenated? Why does the methylenedioxy group rotate?


I've been studying this and have seem to run into some conflicting information.

I have attached a paper below which I will use as reference.

I've noticed when some molecules are methylenated, the methylenedioxy group seems to rotate around the benzene ring, while in other molecules, the methylenedioxy group forms exactly where the OH OH bonds were.

Rotates according to the paper:
2,3-dihydroxybenzaldehyde -> Piperonal
http://www.chemspider.com/Chemical-Structure.81781.html?rid=... > http://www.chemspider.com/Chemical-Structure.13859497.html?r...

I assumed piperonal would come from methylenation of http://www.sigmaaldrich.com/catalog/product/aldrich/284548?l...

4-methylcatechol -> 4-methyl-1,3-benzodioxole.
http://www.chemspider.com/Chemical-Structure.9564.html?rid=5... > http://www.chemspider.com/Chemical-Structure.79904.html?rid=...

With the above molecule I figured 4-methylcatechol would turn into 3,4-methylenedioxytoluene:
http://www.sigmaaldrich.com/catalog/product/aldrich/284548?l...

Does not Rotate:
Catechol -> Benzo-1,3-dioxle
http://www.chemspider.com/Chemical-Structure.13837760.html?r... > http://www.chemspider.com/Chemical-Structure.13881169.html?r...

2,3-hydroxynapthalene -> Naphtho(2,3-d)-1,3-dioxole
http://www.chemspider.com/Chemical-Structure.6824.html?rid=1... > http://www.chemspider.com/Chemical-Structure.88076.html

Looking at the paper attached below, there is a drawing of the mechanism of the methylenation. It makes sense in theory, yet, it does not explain or account for the rotation that occurs in two of the products. How is it meant to be determined whether the methelendioxy group will rotate around the molecule when it occurs?

Attachment: 3489-3490.pdf (110kB)
This file has been downloaded 632 times

[Edited on 20-12-2013 by ChemRaver]

[Edited on 20-12-2013 by ChemRaver]
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[*] posted on 19-12-2013 at 19:15


You must be mistaken about this "rotation." This would be a rearrangement, and in these circumstances, it doesn't happen. For instance, methylenation of 2,3-dihydroxy benzaldehyde would simply give 2,3-methylenedioxybenzaldehyde. Piperonal can be synthesized by methylenating 3,4-dihydroxybenzaldehyde (catechualdehyde).

The mechanism is just a regular SN2 reaction at each phenol oxygen.
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[*] posted on 19-12-2013 at 19:16


.....this might shed some light,....solo


High Selectivity in the Oxidation of Mandelic Acid Derivatives and in
O-Methylation of Protocatechualdehyde: New Processes for Synthesis of
Vanillin, iso-Vanillin, and Heliotropin

Hans-Rene´ Bjørsvik,,Lucia Liguori,
Organic Process Research & Development
2000, 4, 534-543







Abstract:
New synthetic procedures for vanillin, iso-vanillin, heliotropin,
and protocatechualdehyde starting from catechol are described.
The utilisation of statistical experimental design and multivariate
modelling and the mechanistic interpretation of the acid
and base catalysis in the condensation of catechol derivatives
with glyoxylic acid and in the regiocontrolled methylation of
protocatechualdehyde and of the Cu(II) salt catalysis in the
oxidative decarboxylation of mandelic acid derivatives have
allowed the development of new highly selective process.

Attachment: Synthesis.Vanillin.Isovanillin.Heliotropin.pdf (183kB)
This file has been downloaded 736 times

[Edited on 20-12-2013 by solo]




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[*] posted on 19-12-2013 at 19:22


Quote: Originally posted by Crowfjord  
You must be mistaken about this "rotation." This would be a rearrangement, and in these circumstances, it doesn't happen. For instance, methylenation of 2,3-dihydroxy benzaldehyde would simply give 2,3-methylenedioxybenzaldehyde. Piperonal can be synthesized by methylenating 3,4-dihydroxybenzaldehyde (catechualdehyde).

The mechanism is just a regular SN2 reaction at each phenol oxygen.


So is that paper incorrect saying piperonal was recovered via the methylenation of 2,3-dihydroxybenaldehyde?


I was also under the impression that 4-methylcatechol would methylenate to form 3,4-methylenedioxytoluene -> http://www.sigmaaldrich.com/catalog/product/aldrich/284548?l...

Yet the paper says it 'rearranges' into something else (http://www.chemspider.com/Chemical-Structure.79904.html?rid=...)?
---


Thanks Solo, I'll have a look at that

edit:

I don't see how that has to do with what I was asking Solo. Seems like basic reaction preceding there from Catechol -> various derivatives.


[Edited on 20-12-2013 by ChemRaver]
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[*] posted on 19-12-2013 at 19:26



Quote:

I don't see how that has to do with what I was asking Solo. Seems like basic reaction preceding there from Catechol -> various derivatives.



.....not really sure what direction you're going with your line of questions.....solo




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[*] posted on 19-12-2013 at 19:29


Quote: Originally posted by solo  

Quote:

I don't see how that has to do with what I was asking Solo. Seems like basic reaction preceding there from Catechol -> various derivatives.



.....not really sure what direction you're going with your line of questions.....solo


Look at the links in the first post. Those are the molecules claiming were gained via methylenation as per the linked paper. I don't see why the methylenedioxy group ends up shifting which carbons its on half of those molecules, but not on the others?
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[*] posted on 19-12-2013 at 19:52


I am a little confused. All I see in those links are structures and properties. Where does it say, for example in your first link, that piperonal is synthesized from 2,3-dihydroxybenzaldehyde? Maybe you are confused about the naming/numbering? They can either be called methylenedioxybenzenes or benzodioxoles, but numbering is different depending on which name is being used.
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[*] posted on 19-12-2013 at 20:01


There is a PDF attached at the bottom of the OP that I said in the OP that I would be using for reference >.>. In that attached paper all of those molecules I have linked are claimed to have been methylenated and their subsequent products listed.

Am I confused? Would methylenation of 4-methylcatechol not yield 3,4-methylenedioxytoluene? The paper claims otherwise, yet, the diagram for how the reaction precedes contradicts its finds which seem to imply a rearrangement/rotation of where the methylenedioxy group lies.

4-methylcatechol
http://www.chemspider.com/Chemical-Structure.9564.html?rid=5... >

3,4-methylenedioxytoluene:
http://www.sigmaaldrich.com/catalog/product/aldrich/284548?l...



[Edited on 20-12-2013 by ChemRaver]
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[*] posted on 19-12-2013 at 20:36


Oh, I see now. Didn't see that PDF the first time around. That is odd. I'm pretty sure the authors just made a typo. The reactant that gives piperonal should be 3,4-dihydroxybenzaldehyde, not 2,3-dihydroxybenzaldehyde. This is consistent with the mechanism. Everything else in the table looks correct. You are correct; methylenation of 4-methylcatechol (3,4-dihydroxy toluene) would give 3,4-methylenedioxytoluene.
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[*] posted on 19-12-2013 at 20:45


That is what I was thinking, though, if what you are saying is right about the Authors making a typo, then they also made the typo in saying 4-methyl-benzo-1,3-dioxole (4-methyl-1,3-benzodioxole and not 4-methylenedioxytoluene) is the resultant of methylenation of 4-methylcatechol. My question is how could they make 2 major mistakes like that, in terms of reporting the one of the reactants used, as well as one of the products?

Did they simply mix up both of those molecules? IIRC this is not the first incidence that I have seen these indirect claims. The claims that products with a rotated methylendioxy group were yielded from a methylenation, though I do not immediately have any of those sources on hand.

[Edited on 20-12-2013 by ChemRaver]
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[*] posted on 19-12-2013 at 21:11


4-methyl-benzo-1,3-dioxole, 4-methyl-1,3-benzodioxole and 3,4-methylenedioxytoluene are all names for the same molecule. It's just funny (and confusing at first) nomenclature. So those are not mixed up in the paper (though the nomenclature is inconsistent and therefore confusing), and there is still no rearrangement.

If you can find the other sources that cite rearrangement during a methylenation, I would like to see them. As far as my understanding of organic chemistry goes, such a rearrangement is not possible under such mild conditions. The benzene ring is just far too stable. If it actually does happen in some cases, I would be quite eager to learn something new.
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[*] posted on 19-12-2013 at 21:22


I'm glad to hear you say that. I was beginning to doubt my sanity, haha. I didn't think those carbon bonds could just shift like that.
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[*] posted on 20-12-2013 at 05:54


Quote: Originally posted by Crowfjord  
4-methyl-benzo-1,3-dioxole, 4-methyl-1,3-benzodioxole and 3,4-methylenedioxytoluene are all names for the same molecule.

No, they are not all the same. 3,4-Methylenedioxytoluene is regioisomeric to 4-methyl-benzo-1,3-dioxole (4-methyl-1,3-benzodioxole). There are two nomencature errors in the table.




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[*] posted on 20-12-2013 at 12:42


Hey there Nicodem, I was hoping you would peek in. Looks like I still have some confusion on the nomenclature (as did the author of that Tetrahedron paper, apparently).

Okay, I think I get it now, after looking up 4-methyl-1,3-benzodioxole. I forgot that in the fused ring naming, the numbering is like in any heterocyclic. So 3,4-methylenedioxytoluene would be 5-methyl-1,3-benzodioxole. For some reason, I was thinking that the 4 referred to the position on the phenyl ring, but the 1 and 3 still referring to the dioxole ring. It seems the authors of that paper made the same mistake.

Thanks for helping to clear that up, Nicodem.

[Edited on 20-12-2013 by Crowfjord]
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