3
$\begingroup$

I have a question regarding following synthesis which apparently only needs a sour medium to occur: enter image description here

What exactly happens as a mechanism? What I thought was: The alcohol group gets protonated and forms a stable carbocation at it's tertiary position. This charge can now wander to the tertiary carbon next to it; but an H-Shift should not be possible. What is the mechanism here?

$\endgroup$
3
  • $\begingroup$ Ring opens instead of shift. $\endgroup$
    – Mithoron
    Sep 13 '21 at 12:21
  • $\begingroup$ Because of the carbocation in this position? Will it destabilize the ring because it is sp2? $\endgroup$
    – user115162
    Sep 13 '21 at 12:53
  • 1
    $\begingroup$ While acids are indeed sour, the medium is acidic. ;) $\endgroup$
    – user55119
    Sep 13 '21 at 15:17
2
$\begingroup$

I believe the mechanism should be somewhat like this (after the formation of carbocation) -

enter image description here

It would account for the product shown, but I am not sure if it's correct. I feel it's more favourable for a dehydration to occur with the hydrogen from the ring itself (shown on the dash at the top) to form this -

enter image description here

This double bond is conjugated and more substituted, so I should have thought that this would be the major product.

$\endgroup$
5
  • 1
    $\begingroup$ If my mechanism is wrong, please let me know. $\endgroup$
    – TRC
    Sep 13 '21 at 13:31
  • 1
    $\begingroup$ Probably elimination is concerted with ring opening, so "less favorable" product is created. $\endgroup$
    – Mithoron
    Sep 13 '21 at 14:20
  • $\begingroup$ Did the OP's question state that the observed product was the major product? No. $\endgroup$
    – user55119
    Sep 13 '21 at 15:15
  • $\begingroup$ @Mithoron Thanks for the insight. Yes, if it's a single step then to form my proposed product it would need to start making a double bond before the ring was completely broken - which of course would be difficult owing to angle strain. $\endgroup$
    – TRC
    Sep 14 '21 at 3:23
  • $\begingroup$ @user55119 Great point! It shows how reading things closely matters a lot :) $\endgroup$
    – TRC
    Sep 14 '21 at 3:23

Your Answer

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