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Author: Subject: "Unprecedented" reduction of amides
clearly_not_atara
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[*] posted on 10-7-2018 at 11:05
"Unprecedented" reduction of amides


In the course of online discussion of organic synthesis, we are often tempted, but have learned to avoid, proposing a route where an amide is converted by reduction to the corresponding amine. It is conceptually simple, and it makes it much easier to imagine synthesizing all manner of compounds, but the reduction requires -- we thought -- all kinds of very reactive or expensive reagents and forcing conditions, like LAH or DiBAl, so nobody could normally do it. Nobody even thinks about it, because it's impossible.

That is until Das et al published this paper. Zinc acetate and triethoxysilane reduce amides while ignoring ketones, alkenes, azo groups, and almost everything else. Triethoxysilane may be a silane, but it is air-stable and relatively cheap, and the precursor HSiCl3 is also cheap and produced by the direct reaction of hydrogen chloride and silicon.

Tertiary amides only, I'm afraid. Others require more complicated silanes and zinc triflate (later publication, available from https://s3.amazonaws.com/academia.edu.documents/46599081/che... ).

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[Edited on 04-20-1969 by clearly_not_atara]
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Loptr
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[*] posted on 10-7-2018 at 15:50


I think triethoxysilane shows up on eBay from time to time.

I can see this being interesting to some that would want a dialkylated indole starting from that plant hormone.

Interesting none the less.




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byko3y
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[*] posted on 10-7-2018 at 17:30


Yea, but 1 mole of triethoxysilane costs approx 8 times more than a mole of LAH. And you can make aluminium hydrides by a "simple" reaction of sodium hydride with aluminium chloride.
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clearly_not_atara
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[*] posted on 10-7-2018 at 17:41


Trichlorosilane is way cheaper than LAH or triethoxysilane, and the conversion thereof to triethoxysilane is facile. E.g.:

https://patents.google.com/patent/US3985781A/en

Also, LAH is on the SSL:

https://en.wikipedia.org/wiki/DEA_list_of_chemicals#Special_...

Also, blowing HCl (not flammable) over Si to make HSiCl3 sounds a lot easier than blowing H2 (explosive) over molten Na to make NaH. But that's just me. I'm not actually going to do either of those, thanks.

[Edited on 11-7-2018 by clearly_not_atara]




[Edited on 04-20-1969 by clearly_not_atara]
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[*] posted on 11-7-2018 at 04:10


byko3y,
While LAH is cheaper, you aren't getting selectivity and mild reaction conditions. They reduced an amide in the presence of an ester in that paper.
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[*] posted on 11-7-2018 at 11:25


The restriction of LiAlH4 sales, predates current regulations.

Perhaps liability fears, are at the root of this.

Not impossible to find sellers, but not easy either.

The reductions can be achieved via NaBH4 and AlCl3, in Diglyme... But, yields are less than spectacular.

Can this Silane reduction produce Tryptamines? Unknown?
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[*] posted on 14-7-2018 at 00:09


Quote: Originally posted by Loptr  
I think triethoxysilane shows up on eBay from time to time.

Do they ship to individuals though ? I thought they didn't deliver silanes to individuals since they are a fire hazard and transporting them is a huge headache.That was the reason this idea went bust -https://chemistry.mdma.ch/hiveboard/serious/000194986.html

recently I came across a thread-http://www.sciencemadness.org/talk/viewthread.php?tid=84442
where the authors converted an aldehyde to acid and subsequently to an acyl azide.The interesting thing was that they used a reaction originally intended to oxidise alcohols to aldehydes/ketones without further oxidation to acid.

The way they did it was by "disguising" the aldehyde to look like an alcohol(via a bisulfite adduct) to fool the reagents into thinking that they were carrying out the original oxidation of an alcohol to aldehyde,rather than an aldehyde to acid :D

seeing that made me think that if we could make one fuctional group look like another,we could use reactions meant for the 2nd functional group to work on the first.

So in this case,if we could make the amide look like a ketone(by decreasing the electronegativity of the N atom to that of C,for example),we could theoretically reduce amides to amines using wolf kishner. :o
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