4
$\begingroup$

enter image description here

What happens to 1,5-dimethyl-6,8-dioxabicyclo[3.2.1]octane when it is hydrolyzed under acidic conditions?

I know that under acidic conditions the first thing to likely happen is protonation. Does it matter which oxygen is protonated first?

Once that oxygen has been protonated it is going to want to return to neutrality.

Now we have our carbonyl restored (sort of). However, we still want to return to neutrality. Water can attack.

Then we deprotonated the attached water and regenerate the acid-catalyst and we have our original starting compound.

Is this the correct mechanism and is the product correct?

$\endgroup$
  • 1
    $\begingroup$ In your middle structure, you show water attacking the methylated carbon on the left side of the drawing, yet it is the methylated carbon on the right side of the structure that carries some positive charge due to resonance. Examine nucleophilic attack by water at this positive carbon and see what happens $\endgroup$ – ron Oct 18 '14 at 23:45
2
$\begingroup$

Your product is correct, but the mechanism isn't quite right. In the first step, one of the oxygens will be protonated (either is possible). The other oxygen "kicks out" the one activated in the first step. So far so good. However, in the next step, water will attack the "carbonyl" carbon to give a hemi-acetal and a hydroxyl group. Repeating a similar set of steps reveals the ketone and second hydroxyl.

enter image description here

The key difference here is that by adding to the pi system, water reacts with the C-O pi-antibonding orbital, which is the LUMO of the system

$\endgroup$
  • $\begingroup$ Thanks! I had water initially attack on the side you suggested, but I just couldn't see what would happen next! This helps a ton! $\endgroup$ – Dissenter Oct 18 '14 at 23:46

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.