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Author Topic: Possible vinylsulfone to allylsulfone isomerization  (Read 3905 times)

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pgk

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Re: Possible vinylsulfone to allylsulfone isomerization
« Reply #15 on: May 09, 2018, 07:52:29 AM »

A good idea is to preliminary cool it in the refrigerator and thus, the pasty (or waxy) material hardens and cannot easily be absorbed by the filter paper.
But attention when filtering under vacuum:
1). The fast vaporization of the mother liquid under vacuum, quickly absorbs heat and further cools the glassware and thus, ice might be formed during filtration of aqueous suspensions that are excessively cooled < 4oC.
2). The classical Buchner filter with holes and the appropriate round paper filter must be used and not the fried glass disc (sintered glass disc) Buchner filter. 
« Last Edit: May 09, 2018, 09:05:44 AM by pgk »
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Babcock_Hall

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Re: Possible vinylsulfone to allylsulfone isomerization
« Reply #16 on: May 09, 2018, 09:26:33 AM »

Thank you.  Our first target is a six-carbon dicarboxylic acid with a vinylsulfone group in the middle, and we are 2.5 steps into that synthesis, out of four steps.  Our second target is based on a phthalate derivative which is known to be a modest inhibitor.  The vinyl sulfone will branch from the phthalate core.
« Last Edit: May 09, 2018, 12:16:21 PM by Babcock_Hall »
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pgk

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Re: Possible vinylsulfone to allylsulfone isomerization
« Reply #17 on: May 10, 2018, 08:18:53 AM »

1). I wish the best but I don’t see any big problem if working at room temperature and under mild conditions.
2). Getting back to a previous reply, flour is the most common hydraulic powder.
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Babcock_Hall

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Re: Possible vinylsulfone to allylsulfone isomerization
« Reply #18 on: May 16, 2018, 04:07:17 PM »

We have been working at the 100 mg scale.  After acidification with HCl, the first attempt produced only a few milligrams after the filtration.  For the second attempt I advised cooling, but I am given to understand that the recovery was still low.  For the third attempt, we will try to recover the solid by centrifugation using Corex centrifuge tubes.  If that does not work, I am inclined to try to pull the product into ethyl acetate via an extraction.  Does that seem reasonable, or are there better approaches? 
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pgk

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Re: Possible vinylsulfone to allylsulfone isomerization
« Reply #19 on: May 17, 2018, 05:24:23 AM »

1). Extraction is more chemically correct, though centrifugation might be more practical and might lead to slightly higher yield. However, centrifugation does not work in mixtures of isomers because they have the same molecular mass.
2). Are the few milligrams obtained, enough to take a NMR spectrum, in order to see if there is a double bond migration or not and also, if there is a pure product or a mixture of isomers?
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Babcock_Hall

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Re: Possible vinylsulfone to allylsulfone isomerization
« Reply #20 on: May 17, 2018, 05:46:37 AM »

Our model compound is a 3-carbon ester; therefore, isomerization is not possible but it is still useful as a marker of whether or not the vinyl sulfone has stayed intact and as practice before doing a more valuable sample.  With respect to using centrifugation, let me explain my reasoning.  I am concerned that we may be losing material in the filter paper.  Suppose that the hydrolysis has gone to completion and that the acid form is partially but not completely soluble.  Then the solid should be recoverable by centrifugation.  If some of the product (in the acid form) remains in solution, it may be possible to recover this by extraction into ethyl acetate (we used such a technique several years ago when we made BOC-lysyl or BOC-ornithyl nicotinamide or isoniconamide, but our recoveries were never stellar).
EDT
We obtained a H-1 NMR spectrum of the first product, but the signal-to-noise ratio was so poor that we could not be sure whether it was the vinyl sulfone or not.
« Last Edit: May 17, 2018, 06:02:09 AM by Babcock_Hall »
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pgk

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Re: Possible vinylsulfone to allylsulfone isomerization
« Reply #21 on: May 17, 2018, 06:28:35 AM »

You can pre-estimate the aqueous solubility from the logP value and the help of the Yalkovski-Valvani equations:
Estimation of the Aqueous Solubility of Some Acetanilide Derivatives from Octanol-Water Partition Coefficients and Entropies of Fusion,  Acta Farm. Bonaerense, 23(1), 33-38, (2004)
https://pdfs.semanticscholar.org/3031/7e3672b4181eb9aeed25a09cdf4e0495b30e.pdf
The logP value can be estimated with the help of specific software (e.g. ACD/Labs, newer versions of ChemDraw, etc.)
For example, 3-(phenylsulfone) acrylic acid has logP ≈ 0.5 that means hydrophobicity (= negative aqueous solubility), if having a melting point > 60-65oC.
But all the above are simple estimations and the laboratory practice might be a little different.

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Babcock_Hall

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Re: Possible vinylsulfone to allylsulfone isomerization
« Reply #22 on: May 29, 2018, 12:10:19 PM »

What is your reluctance to use acidic hydrolysis to cut the ethyl ester?

If you are willing to get to the methyl ester (easily obtained at any step from the ethyl ester by dissolving in dry methanol and a tiny amount of catalytic sulfuric acid and stirring overnight), there is a well known and nifty trick for very mild anhydrous deprotection of methyl esters: DMF/LiCl. I even found a two year old chemical forums thread you commented on where this procedure is mentioned :P

I can't get access to it right now but here is a microwave version:
https://www.tandfonline.com/doi/abs/10.1080/00397910902778001
I'm sure it has non-microwave procedure for this cited somewhere. PM me if you can't get access or find another lit procedure for DMF/LiCl ester hydrolysis.
With respect to your second paragraph, an alternative strategy would be to make methyl ester from the free acid, brominate, add the sulfone, and deprotect with lithium chloride.  Of course the methyl ester would have to stay intact in the earlier steps.
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