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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: Meter on March 25, 2021, 03:28:34 PM

Title: Synthesis Help: Adding part to terminal alkyene
Post by: Meter on March 25, 2021, 03:28:34 PM
(https://i.imgur.com/LcXGa29.jpg)

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? 
Title: Re: Synthesis Help: Adding part to terminal alkyene
Post by: Meter 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.
Title: Re: Synthesis Help: Adding part to terminal alkyene
Post by: sjb 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?
Title: Re: Synthesis Help: Adding part to terminal alkyene
Post by: Meter on March 26, 2021, 03:08:14 AM
Quote from: sjb 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?
Just the equivalent alcohol?
Title: Re: Synthesis Help: Adding part to terminal alkyene
Post by: Babcock_Hall on March 26, 2021, 02:00:54 PM
An alcohol does not have a good leaving group.
Title: Re: Synthesis Help: Adding part to terminal alkyene
Post by: Meter on March 26, 2021, 02:41:35 PM
Quote from: Babcock_Hall on March 26, 2021, 02:00:54 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?
Title: Re: Synthesis Help: Adding part to terminal alkyene
Post by: Meter on March 26, 2021, 02:46:10 PM
I was thinking either of these two.

(https://i.imgur.com/nXA8ui5.png)
Title: Re: Synthesis Help: Adding part to terminal alkyene
Post by: Babcock_Hall 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.
Title: Re: Synthesis Help: Adding part to terminal alkyene
Post by: Meter on March 26, 2021, 05:19:08 PM
Quote from: Babcock_Hall 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.
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?
Title: Re: Synthesis Help: Adding part to terminal alkyene
Post by: rolnor on March 26, 2021, 05:42:34 PM
What functional group will give an alcohol directly after addition of a carbon nucleophile?
Title: Re: Synthesis Help: Adding part to terminal alkyene
Post by: Meter on March 26, 2021, 05:52:36 PM
Quote from: rolnor on March 26, 2021, 05:42:34 PM
What functional group will give an alcohol directly after addition of a carbon nucleophile?
Aldehyde/ketones ?
Title: Re: Synthesis Help: Adding part to terminal alkyene
Post by: Babcock_Hall 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.
Title: Re: Synthesis Help: Adding part to terminal alkyene
Post by: rolnor on March 29, 2021, 03:53:44 AM
Yes, with a aldehyde you will save one step.
Title: Re: Synthesis Help: Adding part to terminal alkyene
Post by: Meter on April 01, 2021, 03:19:33 PM
Quote from: rolnor on March 29, 2021, 03:53:44 AM
Yes, with a aldehyde you will save one step.
Good to know for the future. Thanks.