The Student Room Group

Tricky organic problem

Have lost the sheet with it on but can remember it:

Compound X reacts with water, toluene (presumably solvent) and heat to form para-chlorophenol.

Compound X has the following spectroscopic data:

C6H6OCl2, so HCl is eliminated in the reaction.
Contains fused 3 and 5 membered rings.

IR 1740 - suggests cyclopentanone ring
1H NMR:
d ~2.5ish (2H, dd, 15.4, 1.4 Hz) (1) - big geminal coupling indicates adjacent to pi system. Smaller coupling probably pseudo axial-pseudo equatorial
d ~2ish (2H, dd, 15.4, 4.3 Hz) (2) - big geminal coupling again. Small coupling probably the pseudo axial-pseudoaxial. Smaller than normal axial-axial as not anti to each other.
d ~1.5ish (2H, dd, 4.3, 1.4 Hz) (3)

These data fit with having the cyclopropane ring in a pseudoequatorial position relative to the 5M ring.

13C NMR
208 (s)
73 (s)
Two more peaks which I can't remember the precise chemical shifts. Both were low (alkyl), one doublet and one triplet.

Propose a structure for X and a mechanism for the reaction.

I think I've got a structure for X but have no idea for the mechanism.

Genuinely no idea.
(edited 11 years ago)
I'd agree with your structure - not alot else it could be :p: I'd take a stab at base-induced enolisation, ring opening and Cl- elimination. Then final tautomerisation to the product.
Reply 2
Original post by EierVonSatan
I'd agree with your structure - not alot else it could be :p: I'd take a stab at base-induced enolisation, ring opening and Cl- elimination. Then final tautomerisation to the product.


Hmm. I don't really like water catalysed enolisation! Although could it go via a hydrate or something similar which might increase the acidity of the alpha proton?
Original post by illusionz
Hmm. I don't really like water catalysed enolisation! Although could it go via a hydrate or something similar which might increase the acidity of the alpha proton?


All you need is a tiny fraction and the reaction will funnel through it. There's a very significant driving force for it to occur (release of ring strain, aromaticity) and a nice high energy environment to overcome kinetic barriers.
Reply 4
Original post by EierVonSatan
All you need is a tiny fraction and the reaction will funnel through it. There's a very significant driving force for it to occur (release of ring strain, aromaticity) and a nice high energy environment to overcome kinetic barriers.


Makes sense I guess. Just never come across a mechanism quite like that. Amazing how much simpler things get when you have more than 10 minutes to think about it and aren't under exam pressures!

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