Comments on: Protecting Groups For Alcohols https://www.masterorganicchemistry.com/2015/06/17/protecting-groups-for-alcohols/ Thu, 10 Apr 2025 16:53:55 +0000 hourly 1 https://wordpress.org/?v=6.9.4 By: James Ashenhurst https://www.masterorganicchemistry.com/2015/06/17/protecting-groups-for-alcohols/#comment-718547 Thu, 05 Dec 2024 15:07:31 +0000 https://www.masterorganicchemistry.com/?p=8979#comment-718547 In reply to gaelle.

Generally no. You can often selectively protect a primary alcohol with a trityl group (triphenylmethyl). There are other situations where you can selectively protect one of the alcohols but unless you are in graduate school it’s not worth getting into them.

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By: gaelle https://www.masterorganicchemistry.com/2015/06/17/protecting-groups-for-alcohols/#comment-718520 Thu, 05 Dec 2024 10:32:01 +0000 https://www.masterorganicchemistry.com/?p=8979#comment-718520 is it possible in a diol to protect only one oh with THP?

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By: James Ashenhurst https://www.masterorganicchemistry.com/2015/06/17/protecting-groups-for-alcohols/#comment-630434 Fri, 17 Jun 2022 22:24:58 +0000 https://www.masterorganicchemistry.com/?p=8979#comment-630434 In reply to Morris.

Dissolve it up in THF or whatever solvent you’re using to make the enolate as a dilute solution (e.g. 0.2 M)

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By: Morris https://www.masterorganicchemistry.com/2015/06/17/protecting-groups-for-alcohols/#comment-630422 Fri, 17 Jun 2022 20:40:58 +0000 https://www.masterorganicchemistry.com/?p=8979#comment-630422 I will try that. Although, the aldehyde is solid and not liquid.

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By: James Ashenhurst https://www.masterorganicchemistry.com/2015/06/17/protecting-groups-for-alcohols/#comment-630421 Fri, 17 Jun 2022 20:37:43 +0000 https://www.masterorganicchemistry.com/?p=8979#comment-630421 In reply to Morris.

Why not just pre-form the enolate with LDA in THF and then add your aldehyde dropwise at low temp? The OH could end up protonating your enolate, but it’s pretty sterically hindered.

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By: Morris https://www.masterorganicchemistry.com/2015/06/17/protecting-groups-for-alcohols/#comment-630419 Fri, 17 Jun 2022 20:30:39 +0000 https://www.masterorganicchemistry.com/?p=8979#comment-630419 A million thanks. You are such a rare gem.
I have tried several times using NaOH, KOH, MgI2, as well as acid catalysis using HCl, but all to no avail (the aldehyde was not deprotonating to form chalcone). I am thinking of using NaH this time around and that’s why am concerned about protecting the hydroxy group.

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By: James Ashenhurst https://www.masterorganicchemistry.com/2015/06/17/protecting-groups-for-alcohols/#comment-630416 Fri, 17 Jun 2022 20:12:02 +0000 https://www.masterorganicchemistry.com/?p=8979#comment-630416 In reply to Morris.

In that case, it would be hard to protect since it’s sandwiched between those t-butyl groups.
Have you tried running the reaction anyways? Do you pre-form the enolate of acetophenone and then add the aldehyde? Curious if the OH would give you problems.
Otherwise this is basically a Claisen-Schmidt reaction, of which about a billion examples exist, under conditions where the enolate forms reversibly and a slight excess of base, I would imagine you could get this to go.

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By: Morris https://www.masterorganicchemistry.com/2015/06/17/protecting-groups-for-alcohols/#comment-630409 Fri, 17 Jun 2022 19:39:49 +0000 https://www.masterorganicchemistry.com/?p=8979#comment-630409 I’m using 3,5-di-tert-butyl-4-hydroxybenzaldehyde. I want to condense it with Acetophenone to form (E)-3-(3,5-di-tert-butyl-4-hydroxyphenyl)-1-phenylprop-2-en-1-one

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By: Morris https://www.masterorganicchemistry.com/2015/06/17/protecting-groups-for-alcohols/#comment-630408 Fri, 17 Jun 2022 19:39:00 +0000 https://www.masterorganicchemistry.com/?p=8979#comment-630408 I’m using 3,5-di-tert-butyl-4-hydroxybenzaldehyde. I want to condense it with Acetophenone to form (E)-3-(3,5-di-tert-butyl-4-hydroxyphenyl)-1-phenylprop-2-en-1-one.

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By: James Ashenhurst https://www.masterorganicchemistry.com/2015/06/17/protecting-groups-for-alcohols/#comment-630407 Fri, 17 Jun 2022 19:36:10 +0000 https://www.masterorganicchemistry.com/?p=8979#comment-630407 In reply to Morris.

Which hydroxybenzaldehyde are you starting with?
The usual procedure would be to start with a methoxybenzaldehyde and then try to remove the CH3 after your aldol with something like TMSI.

One milder way to do it would be to treat the hydroxybenzadehyde with KH and BnBr to make the O-benzylated benzaldehyde and then after your aldol, treat with Pd-C, H2. Or paramethoxybenzyl (PMB) and deprotect with DDQ.

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