[MethylNeptuneAcetate]

Can a reaction like the diels alder reaction occur if the diene is not conjugated, but can have the proper geometric configuration for the same electron transfer?

http://i.imgur.com/sFhLg.jpg

Image of example. A better example might be a compound in which the two double bonds are somehow locked in the proper configuration.

If my question is unclear, I can clarify further if necessary

[Telamond]

I don't think so, the diene needs to be conjugated so that the orbitals are overlapped. If not, they would rather react via a 2+2 mechanism.

[Honclbrif]

I'm not a physical chemist, but I think the orbitals are perfectly capable of overlapping through space, as they are in the correct coplanar orientation. Unfortunately, this reaction requires three free participants to align in the right way, in the same plane, at the same time, which is pretty unlikely. Think spontaneous of formation benzene from acetylene. Closest thing I can think of which resembles this is the Conia-ene reaction http://www.organic-chemistry.org/namedreactions/conia-ene-reaction.shtm or the Pauson-Khand reaction http://www.organic-chemistry.org/namedreactions/pauson-khand-reaction.shtm. Each has fairly isolated participants which proceed through a pericyclic mechanism.


The arrows work, which is rarely a bad sign, but if everything that worked on paper worked in a test tube we would be living in the future right now.

[Honclbrif]

Corrections and retractions. Maybe a better analogy would be the spontaneous formation of cyclohexane from ethylene. Also the Pauson-Khand does not go through a pericyclic mechanism. But either way, you've got the two tethered alkene "arms" which are sill relatively free to move about, and a second alkene equivalent which is also free. Can't say it won't happen, but this reaction would be very entropically disfavorable.