We've learned in class that epoxide ring openings can be catalyized with acids, and I seem to recall either the professor or a classmate mentioning that they also react with bases, but some quick internet searching didn't turn up anything useful. Do epoxide rings react with bases, and if so, what is the mechanism?

(Dis)claimer: this is just for my own curiosity/learning, and not being asked as a homework/test question (yet).


1 Answer 1


Do epoxied rings react with bases

Yes, they can be opened, e.g. with alkoxides.

what is the mechanism?

enter image description here

In principle, this is a $S_N2$ reaction, with the typical approach of the nucleophile from the back side. The difference to a non-epoxide case is that removal of the leaving group (bond breaking, ring opening) is facilitated by the ring strain.

But the general rules for the reactivity of alkyl-substituted centres in $S_N2$ nevertheless apply: the higher the substitution, the lower the rate. This is attributed to the steric hindrance of the respective centre.

Note that the regioselectivity is different under acidic conditions!

  • $\begingroup$ Thanks for the answer! Could you explain why the base attacks the least substituted carbon in basic conditions? Or should I open another question? $\endgroup$
    – kindrobot
    Commented Mar 13, 2015 at 17:39
  • $\begingroup$ @apocryphalauthor Not necessary, the matter of regioselectivity is perfectly within the scope of your question. I've tried to give an explanation in my updated answer. $\endgroup$ Commented Mar 13, 2015 at 17:59

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

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