[beheada]

We just recently touched on Tautomerization, which really fascinated me, but we never thoroughly covered it... more like skimmed over it for principle. I don't know if we're going to go over it any further or not, but I was wondering if there are any classic examples of Tautomerization happening in synthesis? I'm also wondering what mechanism takes place to turn the enol into a ketone/aldehyde (which isn't covered in my specific book).

rayfe

[lavoisier]

Try this to start with:

http://en.wikipedia.org/wiki/Tautomerism

As you will see, tautomerism doesn't occur just in ketones and aldehydes.

[beheada]

Right, wikipedia gives some good information on Tautomerization in general, but I was looking for perhaps an example in synthesis of keto-enol tautomerism and perhaps the mechanism by which it is covered. The TYPE of tautomerization SEEMs to be prototropic since the -H from the alcohol group relocates along with the C-C double-bond, but it still doesn't cover the mechanism of HOW it occurs.

Any examples of ketones (for example) arrived from reduced alkynes or something?

[movies]

Tautomerism happens all the time.  A simple example would be an acid catalyzed aldol reaction where the acid causes a shift in the equilibrium toward the enol form, and that in turn attacks an aldehyde.  There are other examples like the equilibrium of ring closed and ring open lactols.  In some cases you can trap out the ring open form for carbonyl reactions such as Wittig olefination.  Each of these has been used in synthesis many times.

The mechanism of tautomerization is definitely debatable.  In principle, it could be unimolecular, so in the case of keto-enol tautomerism, the proton could just slip along the pi system.  However, you could think of a mechanism where two ketones come into close proximity to one another and then deprotonate one another in an eight membered ring transition state.  At any rate, it's very difficult to observe this mechanism.

[beheada]

Thanks, movies.