[John Mcmurry]

How do I create the cyclopentane without that "extra" bond? I have to use a butane with some kind of terminal groups, right?

[Babcock_Hall]

I would consider reversing the polarities of the two pieces that you are trying to bring together.

[wildfyr]

Oops, I didnt look closely enough. The cuprate route isn't the way to go.

I agree with using butane with 2 terminal groups. Babcock is on the track I was originally thinking. What is another type of chemistry that a methylene alpha to a carbonyl can do? And two carbonyls even better.

[rolnor]

I think if you mix this enone with base you will get dimer or polymer, Michael-addition. Also if you try to remove the carbonyls with Woolf-Kischner you will have attack by hydrazine on the double-bond.

[wildfyr]

That makes this quite a difficult substrate rolnor.

[Babcock_Hall]

Perhaps self condensation (polymerization) could be minimized by the appropriate choice of addition of reagents, but I don't have direct knowledge.  I also wonder whether or not a plausible route, especially if possible side reactions are acknowledged, might be good enough for the purposes of this problem.

[sjb]

How about protection of the double bond - e.g. with Br₂ which you may be able to reduce back off with zinc, or as the epoxide (and then removal with PPh₃?)

Just some random thoughts

[wildfyr]

I'm kicking myself sjb, because I had the exact same two thoughts (bromination or epoxidation), then discarded them because I couldnt think of how to to "deprotect" the double bond correctly.

[sjb]

Hah, I was just looking through some old notes earlier and thought of the thread Not sure about the epoxidation route now I think it through, it is more used to invert the ene geometry so I don't think will be effective here.

[wildfyr]

If you react an epoxide with LAH you'll get an alcohol, which can be dehydrated with a strong acid. That's a nice route.

https://pubs.acs.org/doi/pdf/10.1021/ja01038a042

[rolnor]

I think the epoxide can be converted back to alkene with PPh3 but epoxides are also electrophiles and can react if base is added.