3
$\begingroup$

In the synthesis of (Z)-Jasmone via aldol-condensation as shown below, how can the observed regioselectivity be explained? After all, it is also possible to form the side product shown below. I thought that at least with LDA, the sideproduct should be favored, while I assume that for milder bases such as KOH, the thermodynamic enolate is formed, finally leading to the desired (Z)-Jasmone. Are there any other reasons for the regioselectivity?

enter image description here

$\endgroup$
4
  • 2
    $\begingroup$ The entire reaction (not just enolate formation) is under thermodynamic control, so you get the tetrasubstituted alkene preferentially over the trisubstituted alkene. $\endgroup$
    – orthocresol
    Nov 6 '17 at 12:56
  • $\begingroup$ @orthocresol OK, I see that the the tetrasubstituted ketone is thermodynamically favored, but isn't the last step, i.e. the formation of the unsaturated ketone, effectively irreversible? $\endgroup$ Nov 6 '17 at 17:42
  • 1
    $\begingroup$ The reverse of an E1cb step is conjugate addition of hydroxide to an enone, which isn’t unrealistic. $\endgroup$
    – orthocresol
    Nov 6 '17 at 21:08
  • $\begingroup$ Not only ‘is not unrealistic’ but also rather likely, depending on the conditions involved. I’m too lazy to write up an answer now though … D= $\endgroup$
    – Jan
    Nov 7 '17 at 9:36

Your Answer

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

Browse other questions tagged or ask your own question.