Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: danonki on May 24, 2012, 03:21:33 PM
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Hi everyone!
I'm a second year master student. I'm writting my master thesis in organic chemistry. In one week I have to submit my work, but I still have to run three reactions. Please, I need help. I'm close to cracking up.
So, the problem... I need to generate extra carbon instead of secondary alcohol group. I tried to run tosylation, mesylation and triflation reactions. Nothing works. I think I could try to make halogenation reaction using N-chlorosuccinimide or bromosuccinimide. Which would be better??? And next reaction what I am planning to run is cyanation (instead of halogen [Br or Cl]). What is your experience in this area?
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Hi everyone!
I'm a second year master student. I'm writting my master thesis in organic chemistry. In one week I have to submit my work, but I still have to run three reactions. Please, I need help. I'm close to cracking up.
So, the problem... I need to generate extra carbon instead of secondary alcohol group. I tried to run tosylation, mesylation and triflation reactions. Nothing works. I think I could try to make halogenation reaction using N-chlorosuccinimide or bromosuccinimide. Which would be better??? And next reaction what I am planning to run is cyanation (instead of halogen [Br or Cl]). What is your experience in this area?
Can you please post the reaction you are attempting in general terms, showing the transformation you wish to make. It makes it easier to understand. Thanks
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I have a secondary alcohol. I need to generate extra carbon instead of alcohol group. It could be done in two steps. I tried to make tosylation, mesylation and triflation of alcohol group and I planed to make cyanation (using KCN and 18-crown-6) as next reaction. But nor tosylation, mesylation and triflation didn't work. So, new plan is to make halogenation reaction and after that cyanation reaction.Also my molecule has three stereocenters and I can't lose them. And other end of molecule has C=C double bond which also can't be lost.
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And question is which halogen is more active: chlorosuccinimide or bromosuccinimide. And do you have any suggestions for next (cyanation) reaction?
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What do you mean by "I need to generate extra carbon instead of alcohol group" ? Are you trying to replace the -OH group with a methyl group? Or are you trying to change the -OH group into a leaving group that you can substitute using CN- as a nucleophile?
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I need to replace -OH group with CN group and last reaction will be replacing nitrogen in CN group with C-OH.
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I need to replace -OH group with CN group and last reaction will be replacing nitrogen in CN group with C-OH.
When you said that tosylation etc. dod not work what happened exactly? Did you recover all your starting alcohol?
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After tosylation and mesylation reactions I recovered my starting material ( secondary alcohol). But after triflation reaction I couldn't recover my starting material.
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After tosylation and mesylation reactions I recovered my starting material ( secondary alcohol). But after triflation reaction I couldn't recover my starting material.
Try making a mixed anhydride with iButyl chloroformate then carry out the cyanide reaction.
You may be able to isolate the mixed anhydride.
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There is an other problem. I have only 30mg left of my starting material. :(
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Therefor, I am looking for reaction which must work for secondary alcohols.
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There is an other problem. I have only 30mg left of my starting material. :(
Then make more!!!!
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This is 16 step synthesis! And I am on 13th step.
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This is 16 step synthesis! And I am on 13th step.
Then you are stuck with 30mg fr the mixed anhydride.
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what do you mean by mixed anhydride
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Can you post the actual reaction or at least a partial structure?
With 30 mg, don't use any of it. You are at the stage that you need to run model compounds to ensure the reaction is going to work before you common any of your 30 mg. At least to increase the odds. Either that, or start from scratch again. We don't know if you just used a bad reagent, solvent, technique, etc. Errors come in all shapes and sizes. You need to ensure there wasn't one.
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what do you mean by mixed anhydride
As a prospective Masters candidate you should know this.
RCH2-O(C=O)OR1
This reacts with nucleophiles at the carbon of the RCH2-O group to give CO2 +OR1+RCH2-nucleophile. R1 is usually Iso butyl or t- butyl.
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Can you post the actual reaction or at least a partial structure?
With 30 mg, don't use any of it. You are at the stage that you need to run model compounds to ensure the reaction is going to work before you common any of your 30 mg. At least to increase the odds. Either that, or start from scratch again. We don't know if you just used a bad reagent, solvent, technique, etc. Errors come in all shapes and sizes. You need to ensure there wasn't one.
Don't like model compounds, they usually work, but when you come to use your actual substrate the model conditions usually fail, at least in my humble opinion and experience.
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You might look at oxidizing your alcohol to a ketone and doing a Wittig reaction with (methylmethoxy)triphenylphosphonium bromide. I'm not sure your alkene will surface the subsequent conditions though.
Here is an example:
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It might be useful to see some structure, and post your sulfonation conditions. I've never seen a tosylation/mesylation/triflation at <70% unless it's tertiary - something else must be going on.