Desymmetrization

Desymmetrization in stereochemistry is the modification of a molecule that results in the loss of one or more symmetry elements. An important application involves the introduction of chirality. Formally, such conversion require the loss of an improper axis of rotation (mirror plane, center of inversion, rotation-reflection axis). In other words, desymmetrizations convert prochiral precursors into a chiral products.[1]

Examples

One example is the conversion of cis-3,5-diacetoxycyclopentene to its the monoacetate. In this transformation, the plane of symmetry in the precursor is lost, and the product is asymmetric. The desymmetrization itself is not usually considered useful. The enantioselective desymmetrization however delivers a useful product. This particular conversion utilizes the enzyme cholinesterase.[2]

In another example, transfer hydrogenation converts benzil (PhC(O)C(O)Ph) into one enantiomer of hydrobenzoin:[3]

PhC(O)C(O)Ph + 2 H2 → PhCH(OH)CH(OH)Ph

The precursor benzil has C2v symmetry, and the product has C2 symmetry.

References

  1. ^ Basic Terminology of Stereochemistry, G.P. Moss Ed. Pure Appl. Chem., Vol. 68, No. 12, pp. 2193-2222, 1996.
  2. ^ Donald R. Deardorff, Colin Q. Windham, and Chris L. Craney "Enantioselective Hydrolysis of cis-3,5-Diacetoxycyclopentene: (1R,4S)-(+)-4-Hydroxy-2-cyclopentenyl Acetate" Organic Syntheses, Coll. Vol. 9, p.487 (1998); Vol. 73, p.25 (1996).
  3. ^ Takao Ikariya, Shohei Hashiguchi, Kunihiko Murata, and Ryōji Noyori (2005), "Preparation of Optically Active (R,R)-Hydrobenzoin from Benzoin or Benzil", Org. Synth.: 10, http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=v82p0010