December 09, 2022, 09:06:01 PM
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Topic: silylation and desilylation reviews or information  (Read 7515 times)

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Offline Babcock_Hall

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Re: silylation and desilylation reviews or information
« Reply #45 on: February 01, 2022, 07:28:30 PM »
Fluorine is so small so steric factors are small, its hard to say. Have you tried to add more reagent? As you know, its almost a fool-proof reaction.
We worked the reaction up using Dowex and calcium carbonate.  We could try stirring with a fresh portion of TBAF, but the stoichiometry may be off a bit.

Offline rolnor

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Re: silylation and desilylation reviews or information
« Reply #46 on: February 02, 2022, 12:31:27 AM »
You can do this in very small scale, just enough for a TLC.

Offline Babcock_Hall

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Re: silylation and desilylation reviews or information
« Reply #47 on: February 07, 2022, 09:04:22 AM »
I recently learned that TBAF can come out of a solution in THF at low enough temperature.  I also was advised that this reagent can go bad over time, even in sealed vessels.  I will replace the bottle and be on the lookout for a solid mass in the bottle in the future.

Offline rolnor

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Re: silylation and desilylation reviews or information
« Reply #48 on: February 07, 2022, 11:02:43 AM »
OK, thats typical, you are carefull and put it in refrigerator but it crystalizes…
You will still have fluoride in the solution or? I have used same bottle for long time but offcourse, good to have fresh bottles.

Offline Babcock_Hall

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Re: silylation and desilylation reviews or information
« Reply #49 on: February 07, 2022, 11:41:12 AM »
I warmed it to room temperature with gentle stirring this morning, and everything came back into solution.  However, the age of the solution (now about 11 months) is starting to concern me.

Offline rolnor

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Re: silylation and desilylation reviews or information
« Reply #50 on: February 07, 2022, 11:59:46 PM »
11month does not sound as a problem but you can realy dig deep into this, run one reaction with your old bottle and one with a fresh bottle, then you would be an expert on TBAF-aging.

Offline Babcock_Hall

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Re: silylation and desilylation reviews or information
« Reply #51 on: February 08, 2022, 08:57:39 AM »
It occurs to me that the old THF/TBAF and the reaction mixture could be mixed and the reaction tried again.  I imagine that we will have to perform the whole synthesis over again, anyway, but it would be nice to have some product, even if it were less pure than is ideal.  We are obtaining new TBAF/THF.
EDT
The old bottle is probably slightly more concentrated than it was before, but given all other uncertainties, the difference may not matter very much.
« Last Edit: February 08, 2022, 10:12:19 AM by Babcock_Hall »

Offline rolnor

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Re: silylation and desilylation reviews or information
« Reply #52 on: February 09, 2022, 02:45:21 PM »
You can perform many small scale reactions and just run TLC, it should be clear if the silyl group cleaves from TLC.

Offline Babcock_Hall

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Re: silylation and desilylation reviews or information
« Reply #53 on: February 09, 2022, 05:21:48 PM »
One thing that concerns me is that there are five silylation states (4, 3, 2, 1, or 0 TBDMS groups).  I think we can be certain that a reaction too place by TLC but maybe not how complete it is.

Offline rolnor

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Re: silylation and desilylation reviews or information
« Reply #54 on: February 10, 2022, 01:27:25 AM »
You need a sample of your desired produkt as reference. Yes, you will have a large number of intermediates before you get the completely deprotected you want. You will offcourse need a very polar system to get you polyhydroxy product to move on straightphase TLC, perhaps you need RP-plates.

Offline MOTOBALL

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Re: silylation and desilylation reviews or information
« Reply #55 on: February 11, 2022, 08:48:23 AM »
Have you seen this review article?

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6531329/

Org Biomol Chem. 2019 May 28; 17(20): 4934–4950.
Published online 2019 May 2. doi: 10.1039/c9ob00573k
PMCID: PMC6531329
NIHMSID: NIHMS1027860
PMID: 31044205

Synthesis of carbohydrate building blocks via regioselective uniform protection/deprotection strategies
Tinghua Wang and Alexei V. Demchenko*

Figure 14 may be of relevance/use to your synthesis.

Regards,
Motoball

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