[rgm24]

I know there have been a few posts on this topic (I've been reading for a while... haven't had time to post really until now).
Getting homodimer in my sonogashira... coupling an vinyl bromide w/ TIPS-acetylene, TMS-acetylene, Ph-acetylene.
Polarities of the product and homodimer are basically identical.  Not sure why I keep getting homodimer, but if I could just purify it out I'd be happy for now.  Any purification suggestions?
I've tried two different batches of CuI in neat Et3N and DIPA have both been tried (dist before use, sparged with N2 rigorously).  Tried tetrakis-Pd(0) as well as Pd(PPh3)2Cl2 (basically followed suggestions from past posts, but still homodimer!)
Thanks!

[Dan]

if I could just purify it out I'd be happy for now.  Any purification suggestions?

Chromatography, recrystallisation, trituration, distillation...

Which purification methods have you tried so far?

[g-bones]

how about slow addition of your alkyne to avoid dimerization?

[asa029]

I usually get two products, mainly the heterocoupled (wanted) product and the homocoupled Glaser product. You can degass and purify starting materials all you want, but some homocoupling always seem to occur. You run the reactions in argon of course? Oxygen is the plague of the Sonogashira.

It's hard to know what purification method to use when I don't know the structures, but I usually go for an extraction followed by a flash  using a gradient (EtoAc:hx (1:9)-->(1:1)). This gives the product in excellent purity. In my case the homocoupled dialkyne is very fat-soluble, so some hexane usually washes it away. The ligands are somewhat harder to remove, though...

[nox]

A somewhat roundabout way of doing this is to just take the crude, filter through a pad of Celite to remove any catalyst (and baseline junk), and desilylate everything. Butadiyne is a gas and would just fly out, then it should be much easier to purify your compound. You can reprotect your terminal alkyne if needed.

And if you are going to try this, I strongly recommend desilylating under KF/MeOH conditions. The reaction is extremely clean, >96% yield and no purification needed -- NMR of the "crude" material was simply pristine.

[napoleon79]

Dear Nox,
I like your method that you sue KF/MEOH. Can you describe exactly about this method ? Please. What are you doing next step ? purification ?

Thanks
I am looking forward hearing from you.

Rain

[nox]

The prep was for deprotecting TMS-phenylacetylenes, I'm not 100% sure how general it is but I don't see why it would fail for other substrates. I don't have my notebook with me but the prep goes something like this:

Substrate @ 0.5M concentration in MeOH ("regular grade" is fine, doesn't need to be anhydrous), add 0.6 equiv KF (only used the "anhydrous" version, not the dihydrate) in one portion at room temperature. Stir until deprotection is complete (monitor by TLC). Deprotection is typically complete in <1 hour.

Workup: After TLC indicates complete reaction, dilute with 6x volume of saturated NaCl solution. Extract with Et₂O twice, dry over MgSO4, rotavap off ether. Reactions are typically so clean that no chromatography is needed, but if you're doing some highly sensitive reactions it may be wise to filter it through a plug of silica, since I typically obtain orange to brown products, although the NMR looks absolutely clean.