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Offline zuriel

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Question about two condensation reactions
« on: November 19, 2014, 01:59:43 PM »
Hey everyone.

I have two target structures that I would like to make. One has been made before but utilising tin chemistry which I'd like to avoid for now (if at all possible). The second one I haven't tried anything with yet - but I'll discuss my plans when I get to it and I'd like any experienced chemists here to shoot down my suggestions/give constructive advice where necessary. It'd be VERY much appreciated.

The PNG file is attached with the schemes. The one on top I have tried with LDA and I've also tried with Sodium ethoxide and heat. In the case of the LDA reaction SM was recovered. The attempted condensation with sodium ethoxide only returned decomposed products and some SM. Does anyone have any better suggestions to attain this structure?

The second scheme is one I'd really like to access but I am in the planning stage. For now I'm considering an aldol type condensation with KOH to form the proposed product. Would this be viable? I know someone who worked with mucohalic acids before and basically functionalised both sides using suzuki coupling, which is fine - but the indole boronic acids are SO expensive. I'd like to seek out a more cost-friendly route....again...if it's even possible.

Thanks !!

Offline phth

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Re: Question about two condensation reactions
« Reply #1 on: November 21, 2014, 05:05:48 PM »
pKa of indole is 17 pKa of αCN 28.   You are also creating a 14 π e system. The second reaction will not work without a specific enol equivalent because the aldehyde will add to itself because its more electrophilic than ketone.   Another question, are you quenching rxn or running it on a hot rotovap?  Could be your just allowing the reverse aldol reaction to go if you dont quench it.

Offline zuriel

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Re: Question about two condensation reactions
« Reply #2 on: November 24, 2014, 12:00:10 PM »
pKa of indole is 17 pKa of αCN 28.   You are also creating a 14 π e system. The second reaction will not work without a specific enol equivalent because the aldehyde will add to itself because its more electrophilic than ketone.   Another question, are you quenching rxn or running it on a hot rotovap?  Could be your just allowing the reverse aldol reaction to go if you dont quench it.

Do you think if I had the N-Me version of each SM in the first reaction it might work better?

I haven't tried anything with regard the second reaction yet!  :)

Offline phth

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Re: Question about two condensation reactions
« Reply #3 on: November 25, 2014, 12:59:15 AM »
Well if 2 eq or 3eq LDA give really bad results, then I think suzuki is prolly best. Why don't you just make the borane??

If not I think protecting group is needed.  How would you protect the first α-diketone?  There are multiple ways, and I'm not talking about the nitrogen because it should be reversible enough if a nitrogen occurs

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