[Captain Teemo]

Hi guys,

So I am reacting the phosphonium bromide of Ethyl 4-bromobutanoate with cyclohexanone to get 4-cyclohexylidenebutyric acid in the end.

The procedure is to use potassium tert-butoxide as the strong base to form the carbanions from the phosphonium bromide salt.
The literature says that the solution should turn deep red/orange.

However, in my case, when I added the phosphonium salt (dissolved in DMF) to a suspension of t-OBuK in DMF under Nitrogen, I don't get the deep red solution at all.

What does it suggest?
Have the carbanions been formed?


Thank you!!

[discodermolide]

Try doing the addition the other way round.
Also you can take some of your "ylide solution" and see if it reacts, check by TLC. If it doesn't then add more base.

[Captain Teemo]

Thanks Disco!
i'll try to do that

but the thing is K-tOBu is not soluble in DMF, it makes a kind of suspension and might be hard to do the addition the other way round?

[discodermolide]

I think you can buy solutions in THF, check Aldrich. Also look for "instant ylide".

[Captain Teemo]

Sure, thankss!!

[Eloquentia]

tBuOK should be decently soluble in DMF. The suspension you see might also be of Potassium bromide. Do you use dry enough DMF?  tBuOK is not extremely sensitive to traces of water, but the ylide sure might be.

[zsinger]

Disco beat me to it.  Try, if possible, to ALWAYS make the ylide first, as that is always going to be the reactive species.  Making it first usually precludes it from being messed with in situ .  Hope this helps.
             -Zack

[Captain Teemo]

Thanks so much for your help guys!