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Topic: A Certain m-CPBA Oxidation  (Read 5105 times)

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Offline Wisemanleo

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A Certain m-CPBA Oxidation
« on: May 28, 2008, 12:41:30 PM »
I'm attempting an olide synthesis from a paper by B. Sun (Tetrahedron: Asymmetry 16 (2005) 1305-1307).

The procedure, as stated in the article, is:
Quote
To a solution of  1mmol of 5a ([hydroxyundecyl]cyclopentanone) in 15mL of anhydrous DCM, 6mmol of NaHCO3, and 6mmol of m-CPBA was added. The reaction mixture is then stirred at rt for 4h, and extracted with Et2O. The organic layer was washed successively wit haq. NaHCO3, water, and brine, and dried. After removal of solvent, the crude product was purified by flash chromatography (2:1 petether/EtOAc). 82% yield.

The obstacle I run into every time is that after work up, my product is mostly acid!! My colleague has attempted this too, but to no avail.

Does anyone see any problem with the prep? Or does anyone know a better solution?
Scientia est potentia.

Offline adam

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Re: A Certain m-CPBA Oxidation
« Reply #1 on: May 28, 2008, 01:12:58 PM »
Hi...

Try to purified before use the m-CPBA (the commercial available one normally is 77%, and contains as a impurity the acid---that can hydrolize your lactone).
I know is strange because you use a large amount of hydrogen sodium bicarbonate to neutralize the acid formed...but I tried once an epoxidation (similar reaction conditions) of an alkene with other functional groups sensible to the acid media and the reaction only works well when I purified the peracid before use it.
A good way to purify it, is to wash the peracid (in a DCM solution) with aqueous buffer solution pH=7.5.
good luck.

Offline Wisemanleo

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Re: A Certain m-CPBA Oxidation
« Reply #2 on: May 28, 2008, 04:15:44 PM »
Spot on!! I just reconfirmed the purification method in a book I have. I'll try this out and let you know if it worked out or not.
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Offline Wisemanleo

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Re: A Certain m-CPBA Oxidation
« Reply #3 on: May 29, 2008, 07:58:21 PM »
Well chap, I tried this out, and I still seem to be getting mostly acidic product. I took 1.3grams of m-CPBA (factoring in 77%) and worked it up between DCM and pH 7.5 phosphate buffer. I took the DCM extract and used it in the reaction I'm concerned with (which is already supposed to be done in DCM, so I didn't proceed with drying the DCM extract).

I wonder if 6 equivalents of m-CPBA, as stated in the paper,  is too much? :(

I'll confirm my results soon with HNMR.
Scientia est potentia.

Offline Wisemanleo

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Re: A Certain m-CPBA Oxidation
« Reply #4 on: May 30, 2008, 12:33:20 PM »
NMR shows that there's product, but it's still mostly acid. I'm curious, shouldn't have the work up with sodium bicarbonate gotten rid of any acid?
Scientia est potentia.

Offline adam

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Re: A Certain m-CPBA Oxidation
« Reply #5 on: May 31, 2008, 10:10:37 AM »
ups, it's strange...6 equivalents of peracid acid seems a lot...but if you use an excess of hidrogen sodium carbonate should neutralize it...but I think the problem is the stabilty of the lactone in the reaction media...I guess run the reaction at lower temperature (maybe the lactone resist to hydrolisis) or use an organic base soluble in DCM instead of hidrogen sodium bicarbonate...
I also very upset with experimental section in tethaedron...a lot of times the reactions are not reproducible.

good luck wisemanleo...

Offline Wisemanleo

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Re: A Certain m-CPBA Oxidation
« Reply #6 on: May 31, 2008, 10:45:41 AM »
True! Tetrahedron is disappointing when it comes to that.

I will try using a bit less m-CPBA and this time I'll add it over 10 minutes. Perhaps that will help. Maybe if I have the flask sitting in an acetone-icebath will also help.
Scientia est potentia.

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