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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: kriggy on August 12, 2017, 10:26:53 AM

Title: evans auxiliary
Post by: kriggy on August 12, 2017, 10:26:53 AM

Hi guys, I wonder if any one of you has experience with evans auxililary. Is it possible to coordinate a metal and fix the conformation in case when the amide cant be deprotonated at alpha position? I mean, I have N-substitued derivative of anthranilic acid and I would like to do some reaction on the N-substituent using (pretty much any) auxiliary I didnt check the literature yet because it is just an idea and I dont have much time for it now

(http://i.imgur.com/6Q6Q37x.png)

Title: Re: evans auxiliary
Post by: sjb on August 15, 2017, 11:47:19 AM

Where are you trying to deprotonate and introduce your stereoselectivity?

Title: Re: evans auxiliary
Post by: kriggy on August 15, 2017, 04:34:51 PM

Im trying to do atroposelective cyclization of the of the NH to form variously substitued heterocycles (for example benzimidazole) so I was wondering If I could use it as a source of chirality. Im gonna try more chiral amines or esters but I was wondering about this one. Actualy, no deprotonation in this case.

Title: Re: evans auxiliary
Post by: clarkstill on August 16, 2017, 04:04:35 AM

Sounds like an interesting project.

You can use chiral Cu(II) BOX catalysts for asymmetric 1,4-addition to achiral imides:

J. Am. Chem. Soc. 1999, 121, 7559

The aniline nitrogen might interfere, but definitely worth a go...

Title: Re: evans auxiliary
Post by: kriggy on August 16, 2017, 04:45:32 AM

Thanks for the paper, thats pretty much exactly what I had in mind.

We even tried to introduce the oxazoline into the molecule but the anilin nitrogen interferes with it so we get 1:1 mix of oxazoline and 7 membered ring and I cant realy distinguish them by NMR

Title: Re: evans auxiliary
Post by: rolnor on August 16, 2017, 10:39:31 AM

Is not the acidic proton important to form the adduct? Amid-carbonyls are not very good for coordinating any metal i think, you need some form of enolate, no?

Title: Re: evans auxiliary
Post by: kriggy on August 16, 2017, 10:56:04 AM

Quote from: rolnor on August 16, 2017, 10:39:31 AM

Is not the acidic proton important to form the adduct? Amid-carbonyls are not very good for coordinating any metal i think, you need some form of enolate, no?

Exactly, thats why I asked here if someone can share a thought about this. While amid-carbonyls might not be good at coordinating, authors of the paper by clarkstill do exactly that - coordinate copper with chiral ligand to evans auxiliary of acrylate and then stereoselective diels-alder with quite a succes

Title: Re: evans auxiliary
Post by: rolnor on August 16, 2017, 12:47:05 PM

OK, I should have checked the reference.