Epoxide Reactions: Epoxide Ring opening under Basic Conditions

Epoxides treated with nucleophiles under basic conditions result in the epoxide ring opening:

Under acidic conditions, the nucleophile is added to the less substituted carbon (think “anti-Markovnikov”). This is a short list of potential reagents that would open the ring this way, be sure to look out for basic and not acidic conditions.

The reaction mechanism is depicted below using NaCN and H2O, however, other reagents would likely behave in a similar fashion:

In the first step, lone pair electrons from the negatively charged carbanion from the NaCN molecule attack the less substituted epoxide-carbon atom, sending the free electrons from that bond to the oxygen atom.

In the second step, the negatively charged oxygen deprotonates a nearby water molecule. This creates an OH- molecule, which is the “basic” condition under which this reaction proceeds.

There are many reagents that can be used to open rings however, when nucleophiles are added under basic conditions, an “anti-Markovnikov” like addition occurs, as opposed to acidic conditions where a “Markovnikov” addition occurs.