asymmetric synthesis

Chemical reaction by which unequal amounts of two product isomers are formed.

It is normally not possible to synthesize from materials that do not have optical activity (i.e., are not chiral) one stereoisomer of a chiral compound without the other, but use of a chiral auxiliary, such as an enzyme or other catalyst, a solvent, or an intermediate, can force the reaction to produce predominantly or only one isomer. Asymmetric syntheses are often called stereoselective; if one product forms exclusively, it is stereospecific.

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▪ chemical reaction

      any chemical reaction that affects the structural symmetry in the molecules of a compound, converting the compound into unequal proportions of compounds that differ in the dissymmetry of their structures at the affected centre. Such reactions usually involve organic compounds (organic compound) in which the symmetrical structural feature is a carbon atom bonded to four other atoms or groups of atoms, of which two are alike; in the asymmetric synthesis, one of the identical groups is preferentially modified or replaced, so that the product is a mixture of two dissymmetric compounds, one of which predominates.

      Asymmetric reactions result from the influence of some dissymmetry in the reacting system, such as the presence of a dissymmetric centre in the molecule, a dissymmetric solvent or catalyst, or circularly polarized light, in which the plane of vibration of the electromagnetic fields rotates in either a right-handed or a left-handed sense.

      Asymmetric syntheses often are called stereoselective; if one of the products forms exclusively, the reaction is called stereospecific.

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