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Iqra Mirxa

Mechanism of hydrolysis of polycyclic oxetan

Daniel TerBush  Follow

I have drawn a mechanism but I haven't checked for any references as I am at home now, so it's more like paper chemistry. The chlorine atoms should play some role and possibly disfavour formation of certain carbocations that you would expect in a standard Wagner - Meerwein. It is possible to draw a concerted mechanism (not shown here) but seems very unlikely

**EDIT: I have changed my initial mechanism so it explains better the methyl ester formation (see the comments below). The stereochemistry at C* has also been corrected.

As a general comment you cannot propose a non trivial mechanism without drawing one, it is handwaving. So I did.

Mech2

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Joseph Boyle  Follow
Is there a specific step or steps that you are asking about? In general I tried to use the most stable (looking to me) intermediates and ... get there. Remember also that this is only a suggestion not based on any literature. I did have a quick look today but couldnt find anything relevant, if you or anyone else have any references please postMore
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Ira Spector  Follow
Considering your second proposed mechanism, I find the 3-membered ring closure unlikely. Essentially its a cationic enol ether, which shouldnt be nucleophilic, attacking a carbocation. Put another way, why doesnt water just attack the carbocation directly instead of through an alkene?More
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Jack Brennen  Follow
@ K_P: I dont think step 3 is correct; you show methanol attacking the oxocarbenium ion, but the reaction takes place in water/sulfuric acidMore
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Jesse Raffield  Follow
I dont love this either but you have to end up with the methyl ester somehow, and the most reasonable source is MeOH produced by the initial hydrolysis of the dimethyl ketal. You could probably make it more "believable" by a mechanism that involves an intramolecular attack by the methoxy. Ill have a look later as Im on my mobile now.More
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Jason Shearin  Follow
@ron: I know. Its difficult to draw the polycyclic system in an aesthetically pleasing way.More
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