enter image description here From my notes $\ce{NaNH_2}$ is a good base for the deprotonation of alkynes. After the deprotonation I thought the alkyne would attack the carbon on the cyclopentanone because of the $\delta^+$ charge on the carbonyl carbon due to the EWG effects of the oxygen. Should the protonation of the $\ce{O^-}$ be carried out with conditions specified or can I just leave it as the addition of $\ce{H^+}$?

  • $\begingroup$ There is no such compound as $\ce{NaNH3}$. It is easy to mix up sodium in liquid ammonia $\ce{Na}/\ce{NH3}$ with sodium amide $\ce{NaNH2}$. Make sure you know what you are writing. As for the final workup, you definitely need some kind of proton source. $\endgroup$
    – orthocresol
    Dec 10 '15 at 17:04
  • $\begingroup$ Thank you i must have taken that down incorrectly, ok so would $H_3O^+$ suffice? @orthocresol $\endgroup$
    – MrLuke370
    Dec 10 '15 at 17:20
  • $\begingroup$ Again, please make sure you know what you are writing. If you treat the alkyne with $\ce{Na}/\ce{NH3}$, you are going to get a trans alkene, not the acetylide ion. For the final workup, it depends on how strict your marking scheme is, but I would recommend you write an actual compound like water. You can't go out and buy a bottle of "$\ce{H3O+}$" from Sigma-Aldrich. $\endgroup$
    – orthocresol
    Dec 10 '15 at 17:21
  • $\begingroup$ Ok so would the conjugate acid of the sodium amide protonate the $O^-$? @orthocresol $\endgroup$
    – MrLuke370
    Dec 10 '15 at 17:24
  • $\begingroup$ Or would that be too weak an acid to do so? $\endgroup$
    – MrLuke370
    Dec 10 '15 at 17:43

The route definitely looks feasible and it is more or less what I would have done to arrive at your desired product. A few notes:

  • Make sure you actually have sodium amide $\ce{NaNH2}$ and not sodium in ammonia $\ce{Na/NH3}$. As pointed out in the question comments, they react very differently; the latter generates a trans-alkene.

  • I’m not sure I would have chosen the same base. But the choice of base is likely arbitrary anyway. n-Butyllithium would definitely also do the trick but might be overkill.

  • Typically in a lab setting, reactions with strong bases (as is the case here) are carefully quenched with something aquaeous. So you can be sure that there will be an aquaeous proton source ($\ce{H2O}$ or $\ce{H+/H2O}$, depending on your markers’ preferences) in the end. There should be no need to additionally specify conditions. It would make no sense to attempt to isolate the alcoholate anyway.


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