December 07, 2022, 01:34:36 AM
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Topic: Incomplete silylation with TBDMSOTf/lutidine  (Read 2005 times)

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Offline Babcock_Hall

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Re: Incomplete silylation with TBDMSOTf/lutidine
« Reply #15 on: September 12, 2022, 10:27:37 AM »
Yes, prey is an animal killed by another animal.

The compound in question is orange for some reason, which made cleaning it up a bit easier.

Offline rolnor

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Re: Incomplete silylation with TBDMSOTf/lutidine
« Reply #16 on: September 12, 2022, 01:23:30 PM »
Hm… if it really is orange? Is that possible? Maybe a colored impurity that co-elutes? Othervise I would need a good NMR to confirm the structure.

Offline Babcock_Hall

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Re: Incomplete silylation with TBDMSOTf/lutidine
« Reply #17 on: September 12, 2022, 01:56:18 PM »
It might be an impurity, but we have seen color in previous syntheses.  The structure has an aromatic ring with an aldehyde group and an ether as the two substituents.  We will run the column, and examine the NMR.  The TBS group has very upfield methyl signals, and C-1 of the glycoside is fairly downfield IIRC.  If the spectrum does not look right, we will discontinue work on this batch.

Offline Babcock_Hall

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Re: Incomplete silylation with TBDMSOTf/lutidine
« Reply #18 on: September 19, 2022, 10:16:58 AM »
We ran a column and obtained two pools plus a mixed pool.  Most of the color remained near the top, suggesting that the orange color is an impurity.  One of the pools is probably our product, but there is not enough in my judgement to carry through the next two steps of the synthesis (about 70 mg).  These pools are still useful as TLC standards, and if we had possessed a standard before, we might not have been fooled into thinking that the reaction was incomplete when it almost certainly was complete.  In addition we have now been reminded of the existence of an impurity that has a slightly higher Rf than the product.  We are waiting for another shipment of starting material, which may be here as early as today.
« Last Edit: September 19, 2022, 10:55:14 AM by Babcock_Hall »

Offline rolnor

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Re: Incomplete silylation with TBDMSOTf/lutidine
« Reply #19 on: September 20, 2022, 07:08:27 AM »
I think its claer that my suggestion to use LC-MS would have saved time, money and effort. I know you dont have LC-MS in you departement, I think it would be s good invesment. Very nice that you now have a reference, work will be more efficient.

Offline Babcock_Hall

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Re: Incomplete silylation with TBDMSOTf/lutidine
« Reply #20 on: September 20, 2022, 10:31:13 AM »
We are distilling some commercial lutidine today (it looks yellow), and we will try the reaction later in the week.

Offline Babcock_Hall

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Re: Incomplete silylation with TBDMSOTf/lutidine
« Reply #21 on: October 06, 2022, 11:30:39 AM »
Update:  The silylation went well; after the chromatography however, the product was not quite pure.  If we continue to make products of this kind, my present thinking is to reduce the number of equivalents of TBDMSOTf and to optimize the chromatography (8-10% diethyl ether in hexanes).  The second reaction of the synthesis (Horner) went normally.  We are on the third step, which is desilylation, and we should have a dry and characterized product in a few days.
« Last Edit: October 06, 2022, 11:43:54 AM by Babcock_Hall »

Offline rolnor

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Re: Incomplete silylation with TBDMSOTf/lutidine
« Reply #22 on: October 06, 2022, 11:48:30 PM »
Niiiiice! Great news!

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