Corey–Itsuno reduction

The CBS reduction or Corey - Bakshi -Shibata reduction is a technology developed by chemists Corey, Bakshi and Shibata enantioselective reduction of ketones to the homochiral secondary alcohols. CBS catalyst itself is a chiral auxiliary that is chemically derived from the amino acid proline.

CBS catalyst is used in this reaction as a chiral catalyst in the reduction of prochiral ketones to chiral secondary alcohols. By the use of (S)- CBS, or (R) -CBS, both enantiomers of the alcohol are possible by this reduction.

The reducing agent which is used in a stoichiometric amount of borane ( BH3 ). Borane itself reacts with ketones is slow and mainly unselective. The CBS catalyst serves to activate and on the other providing a chiral environment. It has therefore been present here a so-called ligand- accelerated reaction. The borane hydride is activated by binding to the nitrogen atom of the catalyst and by the complexation of the carbonyl oxygen atom. First, a Lewis acid-base complex of the CBS catalyst and the carbonyl group forms. The electrophilicity of the carbonyl group is thereby sufficiently increased that a reduction with borane is possible. Now the nucleophilic attack on the carbonyl can Hydridatome - carbon atom and enable the reduction. The CBS catalyst provides a unique fixation of the transition state and the hydride ion is preferentially attack from the sterically preferred conformation.

Swell

• Chemical Reaction