Explore · Science · Chemistry

Organocatalysis: Enamine and Iminium Activation

A secondary amine condenses with a carbonyl and changes what that carbon can do: as an enamine it becomes nucleophilic, as an iminium ion it becomes more electrophilic. A chiral amine does both while holding one face of the intermediate shielded.

ages 22 to 238 practice questionsvideo included

What a learner can do afterwards

Draws the enamine and iminium intermediates from a given amine and carbonyl and says which one activates which position
Predicts the sense of induction from the substituent that blocks one face of the intermediate
Explains why the catalyst is released unchanged and what makes turnover fast enough to matter
Compares an organocatalytic route with a metal-catalysed one on cost, air sensitivity and metal residue

1 · Read

A secondary amine condenses with a carbonyl and changes what that carbon can do, so a trace of amine can make a batch without a metal. As an enamine the alpha carbon turns nucleophilic and attacks, while as an iminium ion the beta carbon turns more electrophilic. Each intermediate activates its own position.

Try it together

A chiral pyrrolidine catalyst shields one face of its enamine intermediate. The partner can only approach from the open face, so one product mirror image dominates. After the step, water releases the amine unchanged, and it cycles again.

Turnover stays fast when the catalyst is released cleanly after each step. Against a metal route the trade is clear: metals cost more, dislike air and leave traces in the product, while the small amine is cheap, air-stable and leaves no metal behind.

Good to know

To predict which face reacts, find the bulky substituent on the catalyst and block that face in your drawing. The open face is where the new bond forms.

Enamine activates the alpha carbon, iminium the beta carbon, and a chiral amine picks the face.

2 · Watch

Take it off screen

Print a worksheetA4 with an answer key page for grown-ups. No screen, no internet.

Where it sits

Learn first

Enols, Enolates and Alpha Substitution Asymmetric Catalysis: Where Enantioselectivity Comes From

This opens up

Nothing builds on it yet.

Then practise

8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.

Spotted a problem on this page? Tell us