[nj_bartel]

I was thinking you could maybe cage an alkyne by taking a but-2-yne, replacing the hydrogens with methyl groups (essentially an alkyne with tert-butyl groups on either end), then replacing a hydrogen on each methyl group with a propyl group, which would bridge across to a methyl group on the other side of the alkyne.  I put the model together, and it doesn't seem altogether too unreasonable, except for the fact that if you arrange it in such a way to minimize torsional and angular strain (there's essentially none, it works out pretty well) you end up with some steric strain between one of the hydrogens attached to each 2 position in the propyl bridges and the alkyne.

Any thoughts?

[azmanam]

How are you going to insert into the C-H bond?  That's one of the hot fields in organic chemistry right now, and it's not a trivial task.  Additionally, as the reaction is running and you begin to add methyl groups, a) the steric strain will start to make the last couple of protons essentially inaccessible, and b) what's to keep your base from reacting with the newly installed methyl groups instead of the proton of choice?

[nj_bartel]

I have yet to try to work through a synthesis.  The 'replacing hydrogen' bit I was talking about was just to let you get a picture of the molecule (which is what I was concerned with the viability of, but it seems to look like a possible structure to me.

[sjb]

Do you mean like a propellane? The name Chemdraw gives to what I think is your compound is Tricyclo[5.5.5.2^1,7]nonadec-18-yne. Certainly looks stable enough to me, but again would have no idea how to effectively make the beast...

[Mitch]

nj_bartel: Can you draw the compound you have in mind?

[nj_bartel]

Kind of similar to a propellane, but it would actually have a C=-C inside the cage, not just the bonding electrons.  And yea, synthesis would seem to be a nightmare.

Mitch: (best I can do)  http://img397.imageshack.us/my.php?image=cagedalkynetj0.jpg

[nj_bartel]

Meant to say, another key difference between it and propellane would be the fact that there's no inverterted tetrahedral geometry, though I suppose a more propellane-esque structure could be obtained attempting to synthesize with ethyl bridges rather than propyl.