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Chemistry · Glossary

What is Mannich reaction?

Definition 30.12 University Chemistry — Year 3 · Chapter 30 — Total Synthesis: Strategy and Classic Routes

The Mannich reaction is the addition of an enol or enolate to an iminium ion, made in situ from an aldehyde and a primary or secondary amine, giving a β\beta-amino carbonyl compound.

Robinson’s tropinone synthesis. Two Mannich reactions, the first intermolecular and the second closing the ring, join the three components; the two carboxylic acid groups that made the central CH2 groups enolisable then leave as carbon dioxide. In the bicyclic product the N-methyl bridge spans the seven-membered ring.
Robinson’s tropinone synthesis. Two Mannich reactions, the first intermolecular and the second closing the ring, join the three components; the two carboxylic acid groups that made the central CHX2\ce{CH2} groups enolisable then leave as carbon dioxide. In the bicyclic product the N-methyl bridge spans the seven-membered ring.
Corey’s retrosynthesis of prostaglandin F_2, in outline (double arrows: “is made from”). The two side chains are disconnected first; the cyclopentane with its four stereocentres comes from a lactone, the lactone from a bicyclic ketone, and the ketone from a Diels–Alder reaction that sets their relative configuration.
Corey’s retrosynthesis of prostaglandin F2α\mathrm F_{2\alpha}, in outline (double arrows: “is made from”). The two side chains are disconnected first; the cyclopentane with its four stereocentres comes from a lactone, the lactone from a bicyclic ketone, and the ketone from a Diels–Alder reaction that sets their relative configuration.
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