Stereoselective synthesis

Stereoselective synthesis preferentially forms one stereoisomer over other possible stereoisomers. It controls the three-dimensional arrangement of atoms without necessarily producing a single stereoisomer.

Transition state: A high-energy arrangement of atoms at the boundary between reactants and products in a reaction pathway. Competing transition states often explain why one stereoisomer forms faster than another.
Stereoisomer: One of multiple compounds with the same atom connectivity but different spatial arrangements of atoms. Stereoselective synthesis chooses among these spatially distinct products.
Sharpless asymmetric epoxidation: A titanium-catalyzed reaction that converts allylic alcohols into enantioenriched epoxides. It is a landmark method for setting stereochemistry in oxygen-containing products.
Stereospecific reaction: A reaction in which the stereochemistry of each reactant determines the stereochemistry of its product. Stereospecificity maps substrate stereochemistry to product, unlike preferential product formation alone.
Chiral auxiliary: A temporary chiral group attached to a substrate to direct a reaction toward a preferred stereoisomer. Its three-dimensional structure makes competing reaction approaches energetically unequal.
Enantiomer: One of a pair of stereoisomers that are non-superimposable mirror images. Enantiomeric selectivity concerns preference between mirror-image products.
Sharpless asymmetric dihydroxylation: A catalytic method that adds two hydroxyl groups to an alkene with high enantioselectivity. It creates vicinal stereocenters through selective addition to one alkene face.
Regioselectivity: A reaction's preference for forming one constitutional isomer over other possible isomers. It concerns which positions connect, not the spatial arrangement of atoms.
Asymmetric catalysis: Catalysis in which a chiral catalyst favors formation of one enantiomer over another. It achieves stereoselectivity through a catalyst rather than a temporary substrate attachment.
Diastereomer: A stereoisomer that is not a mirror image of another stereoisomer. Diastereoselective reactions favor one non-mirror-image product over another.

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