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Topic: Synthesis Help: Adding part to terminal alkyene  (Read 877 times)

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Offline Meter

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Synthesis Help: Adding part to terminal alkyene
« on: March 25, 2021, 03:28:34 PM »


Hi all.

I'm a little stumped as to what reagents I need for this step. It's entirely possible that several different reactions are required.

My initial thought was to do some type of "alkylation" to the terminal alkyne using NaNH2 with an appropriate compound, but it seems that those only work for haloalkanes? Anyway I would need a way to add the hydroxyl group as well. Can I get a hint? 

Offline Meter

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Re: Synthesis Help: Adding part to terminal alkyene
« Reply #1 on: March 25, 2021, 05:59:33 PM »
I think I figured it out.

Deprotonate the terminal alkyne with sodium amide, then use the resulting nucleophile for nucleophilic acyl substitution on an appropriate acyl halide, after which it is reduced using something like sodium borohydride.

Offline sjb

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Re: Synthesis Help: Adding part to terminal alkyene
« Reply #2 on: March 26, 2021, 02:28:45 AM »
Is addition to an acyl halide then reduction necessary? Can you use something that corresponds to the reduced acyl halide first?

Offline Meter

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Re: Synthesis Help: Adding part to terminal alkyene
« Reply #3 on: March 26, 2021, 03:08:14 AM »
Is addition to an acyl halide then reduction necessary? Can you use something that corresponds to the reduced acyl halide first?
Just the equivalent alcohol?

Offline Babcock_Hall

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Re: Synthesis Help: Adding part to terminal alkyene
« Reply #4 on: March 26, 2021, 02:00:54 PM »
An alcohol does not have a good leaving group.

Offline Meter

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Re: Synthesis Help: Adding part to terminal alkyene
« Reply #5 on: March 26, 2021, 02:41:35 PM »
An alcohol does not have a good leaving group.
If it's attached directly to a halogen, then the halogen would be the leaving group, no?

Offline Meter

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Re: Synthesis Help: Adding part to terminal alkyene
« Reply #6 on: March 26, 2021, 02:46:10 PM »
I was thinking either of these two.


Offline Babcock_Hall

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Re: Synthesis Help: Adding part to terminal alkyene
« Reply #7 on: March 26, 2021, 04:18:53 PM »
I would question whether or not the structure on the righthand side is a stable molecule.  I am not 100% certain.  There are also some questions in my mind about side reactions, but this particular exercise may not be concerned about such things.
« Last Edit: March 26, 2021, 04:29:57 PM by Babcock_Hall »

Offline Meter

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Re: Synthesis Help: Adding part to terminal alkyene
« Reply #8 on: March 26, 2021, 05:19:08 PM »
I would question whether or not the structure on the righthand side is a stable molecule.  I am not 100% certain.  There are also some questions in my mind about side reactions, but this particular exercise may not be concerned about such things.
No, it was one of those "synthesize A from B using any reagents and starting materials" type questions. I think the acyl halide would be more stable through resonance, no?

Offline rolnor

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Re: Synthesis Help: Adding part to terminal alkyene
« Reply #9 on: March 26, 2021, 05:42:34 PM »
What functional group will give an alcohol directly after addition of a carbon nucleophile?

Offline Meter

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Re: Synthesis Help: Adding part to terminal alkyene
« Reply #10 on: March 26, 2021, 05:52:36 PM »
What functional group will give an alcohol directly after addition of a carbon nucleophile?
Aldehyde/ketones ?

Offline Babcock_Hall

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Re: Synthesis Help: Adding part to terminal alkyene
« Reply #11 on: March 28, 2021, 09:50:32 AM »
Meter, I agree with Rolnor.  My earlier comment was prompted by the presence of an additional functional group, which means that one should consider the possibility of side reactions.  However, I don't have any special knowledge about this particular addition.

Offline rolnor

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Re: Synthesis Help: Adding part to terminal alkyene
« Reply #12 on: March 29, 2021, 03:53:44 AM »
Yes, with a aldehyde you will save one step.

Offline Meter

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Re: Synthesis Help: Adding part to terminal alkyene
« Reply #13 on: April 01, 2021, 03:19:33 PM »
Yes, with a aldehyde you will save one step.
Good to know for the future. Thanks.

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