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Topic: Selective reducing agent. Nitro to amine.  (Read 19341 times)

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Offline 408

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Selective reducing agent. Nitro to amine.
« on: June 14, 2010, 02:43:38 PM »
Hi everyone.

I have had no luck finding a selective reducing agent in the literature.  I have an aromatic azido group, and an amine N-oxide in the same molecule.  I wish to reduce the azido group to an amine.  Does anyone know a reducing agent that will leave the N-oxide intact?

Thanks,
408

Offline 408

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Re: Selective reducing agent. Nitro to amine.
« Reply #1 on: June 17, 2010, 07:58:54 AM »
As much as I hate doing this etiquette wise, *Ignore me, I am impatient*!  Anyone?
Please note the title was meant to say azide reduction, not nitro reduction.  I really doubt there is a method of reducing a nitro group in the presence of an N-oxide.  :P

Offline sjb

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Re: Selective reducing agent. Nitro to amine.
« Reply #2 on: June 17, 2010, 09:13:19 AM »
http://www.jstage.jst.go.jp/article/cl/29/7/29_816/_article may be of some interest - can't see the paper myself, but google abstract seems to include a tantalising "At the same time, azides are selectively reduced in the presence ... tively obtained without any further reduction of nitro group. (entry 4). ..." ?

Offline 408

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Re: Selective reducing agent. Nitro to amine.
« Reply #3 on: June 17, 2010, 11:21:09 AM »
Looks pretty good!  I assume the similarity of a nitro group and a N-oxide means the latter will be left intact...I hope.  I shall try this soon. Thank you.

I think I will just have to try things, due to the semi-rarity of N-oxides I do not think I will find a paper saying "the chemoselective reduction of azides in the presence of N-oxides "

Offline OC pro

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Re: Selective reducing agent. Nitro to amine.
« Reply #4 on: June 17, 2010, 02:27:12 PM »
Generally I donĀ“t trust these Indian Papers. I have seen a lot of scientific fraud. I give that

Much better is it to use 1,3-propanedithiol.  Tet. Lett. 1978, Volume 19, Issue 39, Pages 3633-3634.
It stinks but the reaction proceeds smoothly.



Offline sjb

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Re: Selective reducing agent. Nitro to amine.
« Reply #5 on: June 17, 2010, 03:10:57 PM »
Caveat emptor, of course.

What else is in your molecule, could you afford to reduce it all, then reform the N-oxide?

S

Offline 408

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Re: Selective reducing agent. Nitro to amine.
« Reply #6 on: June 18, 2010, 02:21:46 AM »
Thanks OC, the sulfur route seems highly promising, and the solubility will likely work better for my compound.

sjb: As much as I would like to say my exact molecule, making assistance easier, unpublished work and all that...  Suffice to say the N-oxide is not possible to form when the amine is present using the reaction conditions I have been.

Offline Sam (NG)

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Re: Selective reducing agent. Nitro to amine.
« Reply #7 on: June 18, 2010, 03:19:26 AM »
Should the Staudinger reaction not work for this (Reduction with triphenylphosphine, room temperature)? I had a quick search for reactions between triphenylphosphine and amine oxides, and found this: http://pubs.acs.org/doi/abs/10.1021/ja01515a050 which says that you need a high temperature to get reaction, so I would guess that your amine oxide should be alright at room temperature?

Offline 408

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Re: Selective reducing agent. Nitro to amine.
« Reply #8 on: June 18, 2010, 04:14:31 AM »
The literature method for removal of an N-oxide (ex furoxans to furazans) often involves a PR3 or PX3 species, allowing easy oxide loss by forming the strong P-O bond.  So I had immediately discounted the use of phosphorus agents...  But if temperature control would work, that would be great!  Due to the more difficult work up procedure, I may try this if the stinky method fails.  The produced dithiolane should be easy to separate.

Offline Sam (NG)

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Re: Selective reducing agent. Nitro to amine.
« Reply #9 on: June 18, 2010, 04:44:41 AM »
You definitely know more than me RE: N-oxides so go how you feel.  I just found that paper with a quick search for triphenylphosphine and amine oxide.  I do some work with azides, and I was just offering what I knew from that perspective.

Offline orgopete

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Re: Selective reducing agent. Nitro to amine.
« Reply #10 on: July 03, 2010, 02:00:13 AM »
This isn't based upon anything I know, but I am guessing that it would be easier to break an N-X>N-O>N-N>N-C bond. Hence, I am guessing this is going to be uphill. I would think you could do the reverse selectively, reduce the N-oxide in the presence of an azide.
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Offline tritiger

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Re: Selective reducing agent. Nitro to amine.
« Reply #11 on: July 05, 2010, 08:33:01 AM »
impossible, I think.

N-oxide must be reduced firstly.

you can use different Protecting Groups, then detach them one by one.

Offline 408

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Re: Selective reducing agent. Nitro to amine.
« Reply #12 on: July 13, 2010, 11:30:34 AM »
Orgopete:  But the mass spec of cpds containing both azide and N-oxide show an M-28 peak, and not an M-16 peak :)  So perhaps the N-N bonding is not as strong as you feel :).

I finally got reagents in for the thiol reduction.  So I will know within a week if this works. 

tritiger: based on what?  and what protecting groups would you suggest?

Offline 408

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Re: Selective reducing agent. Nitro to amine.
« Reply #13 on: July 16, 2010, 03:18:38 PM »
Ok, I am running this reaction.  I presume N2 should be eliminated if there is azide reduction occurring.  I have seen nothing yet. 

Perhaps I make more azide oxide, and then also run the staudiger reaction cold if this fails....

Offline 408

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Re: Selective reducing agent. Nitro to amine.
« Reply #14 on: July 24, 2010, 07:41:17 AM »
Amine oxide exists in the mass spec.  The azide oxide is gone. There may have been a small amount of oxide reduction, but that peak is not intense.

This really, really, stinks.  I am attempting to work up the reaction, and all my extracts stink! 


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