[Zainb]

Any help is welcome to explain:
Mechanism of deprotection of TMS-alkynyl compound by K₂CO₃

TMS–C≡C-R + K₂CO₃    H–C≡C-R
~~~~~

[discodermolide]

Any help is welcome to explain:
Mechanism of deprotection of TMS-alkynyl compound by K₂CO₃

TMS–C≡C-R + K₂CO₃    H–C≡C-R
~~~~~

I take it that this is aqueous pot carb?

[Honclbrif]

Silicon loves oxygen almost as much as it loves fluorine.

EDIT: Si can also go pentavalent if attacked by oxygen or fluorine.

[discodermolide]

Silicon loves oxygen almost as much as it loves fluorine.

EDIT: Si can also go pentavalent if attacked by oxygen or fluorine.

But there must be a proton source in this example.

[Honclbrif]

Excellent point. I was assuming it was aqueous (or water-THF/MeOH/ACN/whatever).

[Zainb]

The used solvent is methanol which firstly reacted with K₂CO₃ to give potassium methoxide CH₃O^-K⁺

[fledarmus]

The used solvent is methanol which firstly reacted with K₂CO₃ to give potassium methoxide CH₃O^-K⁺

Really? From the pK_as, that looks to me to be about five orders of magnitude in the wrong direction. Do you think there would be any significant concentration of methoxide in this solution?

[Zainb]

http://pubs.acs.org/doi/abs/10.1021/je020012v

in this paper, there are more explanation on the solubility of potassium carbonate in the methanol.

[discodermolide]

http://pubs.acs.org/doi/abs/10.1021/je020012v

in this paper, there are more explanation on the solubility of potassium carbonate in the methanol.

In that case the mechanism of de-silylation becomes obvious. In fact it should be catalytic in base.
Do you have any ideas?

[Zainb]

In that case the mechanism of de-silylation becomes obvious. In fact it should be catalytic in base.
Do you have any ideas?

TMS-acetylenes can removed under basic conditions

K₂CO₃ + 2MeOH  2K^+-OMe + H₂O + CO₂

^-OMe  will attack Si to give pentavalent coordination intermediate..

[discodermolide]

In that case the mechanism of de-silylation becomes obvious. In fact it should be catalytic in base.
Do you have any ideas?

TMS-acetylenes can removed under basic conditions

K₂CO₃ + 2MeOH  2K^+-OMe + H₂O + CO₂

^-OMe  will attack Si to give pentavalent coordination intermediate..

And the proton originates from the methanol regenerating methoxide which is what I meant about being catalytic in base.

[Zainb]

Still not clear if the triple bond will contribute in the breaking of the bond (with red colour) Si–C≡C in the structure TMS–C≡C-R.

[discodermolide]

Still not clear if the triple bond will contribute in the breaking of the bond (with red colour) Si–C≡C in the structure TMS–C≡C-R.

No contribution from the triple bond.
The nucleophile attacks the Si atom and the electrons from the C-Si bond pick up a proton from the solvent, which is why I said it is catalytic in base.

[Zainb]

The solvent is MeOH...

Thanks a lot discodermolide.

[nelson correia]

Hello

You can show a complete mechanism of this reaction please.
Thanks