Advanced Topic 847 of 1102 Organic Chemistry
Asymmetric Synthesis
Methods to make a single enantiomer using chiral catalysts or auxiliaries.
In-depth explanation of Asymmetric Synthesis
Asymmetric synthesis is the preparation of a compound in which one enantiomer is formed in excess over the other. It is achieved using chiral catalysts, chiral auxiliaries that are temporarily attached to the substrate, or chiral reagents, which create a diastereomeric transition state of lower energy for one pathway. The success is measured as enantiomeric excess, which is the difference between the two enantiomers as a percentage of the total. The method is important because the two enantiomers of a drug can have very different biological effects.
Going deeper: Asymmetric Synthesis
Key ideas: Making one enantiomer in excess using chiral auxiliaries, chiral catalysts (Sharpless, BINAP-Ru hydrogenation, organocatalysts like proline) or chiral pool starting materials. Success is measured by enantiomeric excess (ee, e.g. 98 percent ee means 99:1). A chiral catalyst lowers the activation energy of one diastereomeric transition state; difference of 4 kJ/mol gives about 5:1 selectivity at room temperature.
Common mistakes and connections: Students think any chiral catalyst gives pure product, ignoring ee. Another error is believing that the product from achiral reagents can have optical activity; it will be racemic. Links to enantiomers, drug development and Sharpless epoxidation.
Visualization of Asymmetric Synthesis
A larger energy difference between competing transition states gives a higher enantiomeric excess; about 10 kJ/mol gives about 96 percent ee. The interactive lesson shows this as a live animation or chart.
Worked example and use case
L-DOPA, a drug for Parkinson's disease, is made by asymmetric hydrogenation to give the single active enantiomer.
Frequently asked questions about Asymmetric Synthesis
What is Asymmetric Synthesis?
Methods to make a single enantiomer using chiral catalysts or auxiliaries.
Is Asymmetric Synthesis a beginner, intermediate or advanced topic?
Asymmetric Synthesis is a advanced topic in Organic Chemistry. It builds on beginner and intermediate topics, so review those first if needed.
What should I learn before Asymmetric Synthesis?
Study these earlier topics in Organic Chemistry first: Woodward-Hoffmann Rules, Cross-Coupling Reactions, Olefin Metathesis.
What comes after Asymmetric Synthesis?
The next topics in Organic Chemistry are Green Chemistry Principles and Heterocyclic Compounds.
Can I practise Asymmetric Synthesis with quizzes?
Yes. The interactive lesson includes a self-check question on Asymmetric Synthesis, and the Organic Chemistry quiz draws on every topic in this area.
Where Asymmetric Synthesis fits in Organic Chemistry
Asymmetric Synthesis is topic 119 of 148 in Organic Chemistry.