Chiralpedia

Absolute Asymmetric Synthesis
Definition: Formation of an enantiomeric excess without any chiral influence (no chiral reagents or fields).
Context: Mechanistic interest and potential origin-of-chirality implications.
Example: Soai asymmetric autocatalysis.
Related Terms: Asymmetric Amplification, Soai Reaction.
Reference: Soai, Nature (1995).

Asymmetric Synthesis (Chiral Synthesis)

Alternative Strategy: Chiral Separation

Definition: A chemical synthesis that preferentially forms one enantiomer or diastereomer over the other, resulting in an enantioenriched or enantiopure product through the use of a chiral source such as a chiral catalyst, chiral reagent, chiral auxiliary, enzyme, or substrate.
Context: Asymmetric synthesis is one of the principal strategies for producing optically active compounds without resolving a racemate. It is widely employed in the pharmaceutical, agrochemical, and fine chemical industries to prepare single-enantiomer products with high enantiomeric excess (ee). Advances in asymmetric catalysis, organocatalysis, biocatalysis, and transition-metal catalysis have made asymmetric synthesis an indispensable tool in modern drug discovery and manufacturing.
Example: The asymmetric hydrogenation of prochiral alkenes using the chiral BINAP-ruthenium catalyst, developed by Ryoji Noyori, produces enantiomerically enriched products and has been widely applied in the industrial synthesis of pharmaceuticals.
Related Terms: Asymmetric Catalysis, Chiral Catalyst, Chiral Auxiliary, Chiral Reagent, Enantioselective Synthesis, Stereoselective Synthesis, Chiral Resolution, Kinetic Resolution.
Reference: Noyori, R. (1994). Asymmetric Catalysis in Organic Synthesis. John Wiley & Sons, New York. ISBN: 978-0471351970; Ojima, I. (Ed.). (2013). Catalytic Asymmetric Synthesis (3rd ed.). John Wiley & Sons. ISBN: 978-1118390055; Walsh, P. J., & Kozlowski, M. C. (2009). Fundamentals of Asymmetric Catalysis. University Science Books. ISBN: 978-1891389543; Knowles, W. S. (2003). "Asymmetric Hydrogenations (Nobel Lecture)." Angewandte Chemie International Edition, 42, 2-9. International Union of Pure and Applied Chemistry. Compendium of Chemical Terminology (Gold Book) - Entries on asymmetric synthesis and stereoselective synthesis.
Key Distinction
Asymmetric Synthesis (Chiral Synthesis): Produces one stereoisomer preferentially from achiral or prochiral starting materials using a chiral influence.
Stereoselective Synthesis: Preferentially forms one stereoisomer over another but may involve either enantiomers or diastereomers and does not necessarily require a chiral source.
Enantioselective Synthesis: A type of asymmetric synthesis that preferentially produces one enantiomer.
Chiral Resolution: Separates existing enantiomers from a racemate rather than creating chirality during synthesis.
Key Insight:
Asymmetric synthesis creates chirality during the synthetic process by favoring the formation of one stereoisomer. In contrast, chiral resolution separates stereoisomers that have already been formed. Asymmetric synthesis is generally more atom-efficient and can theoretically achieve 100% yield of the desired enantiomer, making it the preferred strategy for the industrial production of many modern single-enantiomer pharmaceuticals.

Chiral Pool Synthesis
Definition: Use of abundant natural enantiopure building blocks as stereochemical sources.
Context: Efficient, scalable strategy in pharmaceutical synthesis.
Example: Use of L-amino acids to set stereochemistry.
Related Terms: Biocatalysis, Chiral Auxiliary.
Reference: Morrison & Boyd.

Enantioconvergent Synthesis
Definition: Both enantiomers of a racemic starting material are transformed into one enantiomeric product.
Context: Maximizes material economy in process chemistry.
Example: Ni-catalyzed cross-couplings with stereoretention.
Related Terms: DYKAT, Stereoretentive Coupling.
Reference: Fu, Acc. Chem. Res. (2017).

Stereodivergent Synthesis
Definition: Strategy enabling access to multiple stereoisomers via controlled catalyst/condition changes.
Context: Efficient generation of stereochemical arrays for SAR.
Example: Catalyst-controlled divergent aldol products.
Related Terms: Enantiodivergence, Diastereodivergence.
Reference: Wang & List, Angew. Chem. (2012).

Syn (Stereochemical Descriptor)

Paired Concept: Anti-(Stereochemical Descriptor)

Definition: A stereochemical descriptor indicating that two substituents, atoms, or groups are located on the same side of a reference plane, bond, ring system, or molecular framework.
Context: The term syn is commonly used in stereochemistry to describe the relative spatial orientation of substituents in organic molecules and reaction products. It is frequently encountered in conformational analysis, addition reactions, eliminations, and carbohydrate chemistry. In reaction mechanisms, syn addition refers to the simultaneous addition of two groups to the same face of a double bond, whereas syn elimination involves the removal of groups from the same side of a molecular framework.
Example: The syn dihydroxylation of an alkene using osmium tetroxide (OsO₄) produces a vicinal diol in which both hydroxyl groups are added to the same face of the double bond.
Related Terms: Anti, Syn Addition, Syn Elimination, Relative Configuration, Stereochemistry, Diastereomer.
Reference: Clayden, J., Greeves, N., & Warren, S. (2012). Organic Chemistry (2nd ed.). Oxford University Press; Eliel, E. L., Wilen, S. H., & Doyle, M. P. (1994). Basic Organic Stereochemistry. John Wiley & Sons; Carey, F. A., & Sundberg, R. J. (2007). Advanced Organic Chemistry, Part A: Structure and Mechanisms (5th ed.). Springer; International Union of Pure and Applied Chemistry. Compendium of Chemical Terminology (Gold Book) - Entries on syn/anti descriptors and stereochemical terminology.
Key Distinction
Syn: Groups are oriented on the same side of a reference plane or molecular framework. Anti: Groups are oriented on opposite sides of a reference plane or molecular framework. Syn Addition: Two groups add to the same face of a multiple bond. Anti Addition: Two groups add to opposite faces of a multiple bond.
Key Insight:
Syn is a relative stereochemical descriptor that describes spatial relationships between groups. Unlike absolute descriptors such as R/S or P/M, it does not specify the absolute configuration of a molecule.

Synclinal
Definition: Conformation where substituents on adjacent atoms have a dihedral angle of 0°-90° (commonly ~60°).
Context: Equivalent to gauche arrangement; denotes closeness in space.
Example: Synclinal butane conformation (~60° torsion angle).
Related Terms: Antiperiplanar; Gauche; Conformer.
Reference: Eliel & Wilen (1994).