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Topic: Help troubleshooting a Buchwald-Hartwig amination?  (Read 2556 times)

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Offline minimumlong3

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Help troubleshooting a Buchwald-Hartwig amination?
« on: September 06, 2018, 04:55:31 PM »
Does anyone have any experience in Pd cross-coupling reactions that could help me? I'm trying to couple an aryl chloride (that has a alcohol protected by a TBDMS and an heterocycle) with a alkylamine with a phenol at the end of it. I'm getting weird products (multiple TBDMS signals when there should only be one). Also, my "product" tends to have a higher Rf than both of my reagents, if someone knows anything about this I would be very grateful!

Offline kriggy

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Re: Help troubleshooting a Buchwald-Hartwig amination?
« Reply #1 on: September 08, 2018, 04:45:41 AM »
Why shouldnt it have higher Rf thatn your reagents?
Also, what are your conditions? Do you have any idea what is the structure of your by-product? The TBDMS signals could come from your product and unreacted starting material?

You probably need to provide us with more information

Offline wildfyr

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Re: Help troubleshooting a Buchwald-Hartwig amination?
« Reply #2 on: September 08, 2018, 07:41:29 AM »
What do you mean multiple tbdms signs? Tbdms gives 2 peaks on nmr. 9H:6H at about 0.12 and 0.03 ppm in Cdcl3 if memory serves. If you ha e starting material and product that quickly can become 4 very close peaks. If you have vacuum grease in there it will confuse things as well.

I also echo kriggy's first question.

Offline phth

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Re: Help troubleshooting a Buchwald-Hartwig amination?
« Reply #3 on: September 11, 2018, 10:19:26 PM »
Doubling of signals is commonly due to the formation of a chiral molecule from an achiral molecule.

Offline kriggy

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Re: Help troubleshooting a Buchwald-Hartwig amination?
« Reply #4 on: September 12, 2018, 02:55:17 AM »
Thats not entirely true. You cant distinguish enantiomers in NMR to do so, you need to conver them into diastereomers. So in case one is making an racemic or enantioenriched mixture, then there is nothing visible in common NMR experiment.

Offline phth

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Re: Help troubleshooting a Buchwald-Hartwig amination?
« Reply #5 on: September 19, 2018, 01:26:49 AM »
Thats not entirely true. You cant distinguish enantiomers in NMR to do so, you need to conver them into diastereomers. So in case one is making an racemic or enantioenriched mixture, then there is nothing visible in common NMR experiment.

Protons/other groups become diastereotopic and thus unequal in energy upon formation of 1 chiral center.

Offline kriggy

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Re: Help troubleshooting a Buchwald-Hartwig amination?
« Reply #6 on: September 21, 2018, 02:32:33 AM »
Oh I see, youre right, I didnt undertand your previous post correctly.

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