[kayenta]

Hi everyone, my first post here.

I was hoping someone could briefly outline the stereoselectivity of epoxide ring openings, specifically if you are opening cyclohexene oxide under acidic conditions with a weak nucleophile (EtOH), what would be the stereochemistry of the product (ie cis or trans-2-ethoxycyclohexanol) and why?

Thanks in advance.

[OC pro]

Any ideas yourself?

[kayenta]

Well, my instinct that the alcohol will attack from below the epoxide ring to form the trans product, but I'm not sure.

Also, would the stereoselectivity be different if the ring is opened by a good nucleophile without acid catalyst?

[OC pro]

Your instinct is right. Strong nucleophiles will attack from the back side via Sn2. Weak nucleophiles need acid catalysis via Sn1. This also gives trans products, but the regiochemistry can be different.

[kayenta]

Cool, thanks!