[sarahami]

Hey,
Is it possible to explain a little bit about the work up of Sonogashira coupling? I am totally confused. I set up the reaction, I got the nmr from mixture. It seems OK but little impurity. I washed it with pentane, and ran column, after column I didn't get anything. I am so depressed. Thank you all!

[Honclbrif]

Did your material degrade on the column, or did you just fail to wash your product out of the column?

[sarahami]

Hi,
The thing happened is, what I got from thcolumn is not what I supposed to get. It is not like the actual nmr. It is totally different and very impure. I used Alumina basic. Can it make any problem?
Thank you very much for your response.

[nox]

Without any details it's pretty much impossible to give any specific advice.

[Honclbrif]

Try a forum search for "Sonogashira coupling", there's been quite a few discussions on it, one of those threads may have something of use to you as they cover a lot of common problems and solutions.

[sarahami]

Hi,
I just explain my problem with details,
I set up reaction with 4-bromobenzaldehyde and trimethylsilylacetylene, and the reaction worked fine, because I got a little bit impurity in NMR, I just set the column to purify it. and also for work up I used hexane.
After column I just got weird stuff in my nmr.

[asa029]

Are you sure that nothing is left in the collumn? Either your product  washed out before you started taking fractions or it's still left in the collumn when you finished taking fractions. Always make sure to wash through the collumn with a more polar eluent when you think you're done, just to make sure. Nothing's worse than a collumn full of your product. If you're sure no compounds are left, it sounds like it degraded or that you lost it during your washings. Does spots on the  TLC of the crude correspond to all the spots you find in your fractions?

For work-up in Sonogashira I usually do an extraction first (Et₂O with three water washes) to get rid of pesky salts and then collumn. I use traditional silica with gradient EtOAc and hexanes starting from 1:9 and working my way up to 1:1, but my molecules are pretty polar.

Hope this helps.

[superg]

hi,

i've done this coupling before, working really well. the reaction mixture was taken to dryness, the residue extracted with ether, washed with water.
column on silica, using hexane/DCM 3/2 as eluent. crude (black oil) adsorbed on silica before. if you elute just with hexane, you will just collect the homocoupled alkyne. the compound elute as a yellow/brown band, with some residual sarting bromo right after if the reaction hasn't gone to completion.
it is a brown solid after evaporation with characteristic smell of benzaldehyde derivative. got 95-99% yield on several run on 10g scale of starting bromo.

i hope this will help

[sarahami]

I really thank you!!!

[Nosterius]

TMS-protected acetylenes are very sensitive under basic conditions (usual deprotection conditions are K2CO3 in MeOH).

Have you considered if your solid support (basic alumina) could deprotected your alkyne? Look into your 1H NMR spectra for a small singlet in the acetylenic region.

Good luck!