[nielsgeode]

I need to synthesize compound B or C (I can make B from A with 2 eq of nBuLi)

I have synthesized A (pure, including elemental analysis) and tried to convert it to C with 2 eq of MeLi, however this gives D. I then tried to react A with one equivalent of MeMgCl. After analysing this (it gave E) I added a second equivalent to my reaction mixtur (after cooling down again to -78). This second equivalent did not react. What I then tried was cooling down again and adding one eq of MeLi (after my 2 eq of MeMgCl) but again: no reaction.

Anyone any suggestions for this or maybe a complete different route to compound B or C where you avoid the fulvene moiety and hence the formation of D?

Thanx
Niels

[macman104]

Can you selectively reduce the "exocyclic" double bond?  The other bonds are all aromatic, so should not be as reactive I think...

[sjb]

What would happen if you were to react NaCp with 2-bromo benzoylchloride, and then methylenate?

I'm a bit worried you may get a horrible mixture of cyclopentadiene isomers

[nielsgeode]

What would happen if you were to react NaCp with 2-bromo benzoylchloride, and then methylenate?

I'm a bit worried you may get a horrible mixture of cyclopentadiene isomers

In my opinion this would give you this?



with respect to the double bond isomers: I don't care at all because I will deprotonate it afterwards with BuLi again to give me this:



I did this with similar (fulvene) systems where the other route (addition of MeLi, quenching, column, deprotonate with BuLi) works 100% fine. There where indeed several double bond isomers of the Cp formed but that doesn't matter

[macman104]

I don't want to repoint out what I thought, but is there something I am missing about selectively reducing the non-aromatic double bond and giving you C?

[nielsgeode]

I don't want to repoint out what I thought, but is there something I am missing about selectively reducing the non-aromatic double bond and giving you C?

You mean the C=C bond between the two rings? As you can see I tried this with methyllithium but instead of adding to this bond it abstracts a proton from the methyl group on the bridging carbon...

[macman104]

Apologies, I had never heard of MeLi used as a reducing agent.  I was asking more simply does something like H2/Pd, not work, as I know under low pressure, things like Benzene don't get reduced, but I wasn't sure if things like Cp were reduced under those conditions.

[nielsgeode]

I think so yes, this thing behaves like a fulvene, not like a cp. Fulvenes are quite reactive. Secondly: I need two methyl groups, not two protons

[macman104]

So...where do you want the final methyl?  You want one attached to the ring?

This is how I followed you:

Goal:  You need to make B or C (which you can already do with 2 eq. of BuLi from A).

Attempts:  Now you tried to convert A to C with 2 eq. of MeLi, but you get D
So then you tried to convert A to C with 1 eq of MeMgCl, which gave you E.
With E in hand, you tried to salvage it by adding one more MeMgCl, but you had no reaction.
You threw another potion at it (this time MeLi), you had no reaction again.

So now you want to find a route to B or C, that avoids the fulvene moiety?

So I said, "ok, if I had D, C is just the 'H2' looking reduced form of D".  So I was asking if there was something I'm missing about the reaction.  Because I reasoned that the double bond that was not part of either aromatic moiety would be much more susceptible to reduction than the two rings which would then give you C, which is what you needed.

I believe sjb, was saying, you can make D directly through his reaction and then wittig the methyl group on, and then reduce, possibly?

How did I do on understanding the thread?

[sjb]

Actually, I misunderstood as well, I thought you were after alternate ways to D , to then reduce a la macman to C. Not sure how you'd chemoselectively reduce the tetrasubstituted double bond over the two cyclic ones though - is this something for Wilkinson's catalyst? I don't think the Cp double bonds are aronatic here - 4pi electrons?

I'm not sure Wittig is the way to convert C=O to C=CH₂ here, given the comparable basicity of the ylid and the Cp ring (imo), how about Tebbe, or Pedersen?

S

[nielsgeode]

Ow sh*t  I forgot to draw one methyl in a hurry. I updated the picture 

*I see that I can no longer edit my first post so I updated it again. My apologies for this mistake
So I need B or C (I can make B from C with 2 eq of BuLi)

[macman104]

Actually, I misunderstood as well, I thought you were after alternate ways to D , to then reduce a la macman to C. Not sure how you'd chemoselectively reduce the tetrasubstituted double bond over the two cyclic ones though - is this something for Wilkinson's catalyst? I don't think the Cp double bonds are aronatic here - 4pi electrons?

Sorry, you are correct, I was confusing the Cp ring with the anion (which is aromatic).