Asymmetric catalytic reduction is the use of various chiral catalysts to reduce a prochiral

Prochiral

In stereochemistry, prochiral molecules are those that can be converted from achiral to chiral in a single step.If two identical substituents are attached to a sp3-hybridized atom, the descriptors pro-R and pro-S are used to distinguish between the two...

 organic compound to obtain a chiral product. This is one of the several techniques used in chiral synthesis

Chiral synthesis

Enantioselective synthesis, also called chiral synthesis, asymmetric synthesis or stereoselective synthesis, is organic synthesis that introduces one or more new and desired elements of chirality...

.

Typically, a transition metal

Transition metal

The term transition metal has two possible meanings:*The IUPAC definition states that a transition metal is "an element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell." Group 12 elements are not transition metals in this definition.*Some...

 is used with a bulky chiral ligand to such that the substrate molecule can only approach in a particular orientation. This causes an external reductant to reduce the substrate in a predictable fashion. Well-known examples include Knowles

William Standish Knowles

William S. Knowles is an American chemist. He was born in Taunton, Massachusetts. Knowles was one of the recipients of the 2001 Nobel Prize in Chemistry. He shared half the prize with Ryōji Noyori for their work in asymmetric synthesis, specifically for his work in hydrogenation reactions. The...

' ruthenium

Ruthenium

Ruthenium is a chemical element with symbol Ru and atomic number 44. It is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum group, ruthenium is inert to most chemicals. The Russian scientist Karl Ernst Claus discovered the element...

-based catalyst, similar to Wilkinson's catalyst

Wilkinson's catalyst

Wilkinson's catalyst is the common name for chlorotrisrhodium, a coordination compound with the formula RhCl3 . It is named after the late organometallic chemist and 1973 Nobel Laureate, Sir Geoffrey Wilkinson who popularized its use.-Structure and basic properties:The compound is a square planar,...

, which reduces alkenes, and Noyori asymmetric hydrogenation

Noyori asymmetric hydrogenation

The Noyori asymmetric hydrogenation is a chemical reaction described as an asymmetric reduction of β-keto-esters.Both enantiomers of BINAP are commercially available and widely used...

 catalysts using chiral BINAP

BINAP

BINAP is an abbreviation for the organophosphorus compound 2,2'-bis-1,1'-binaphthyl. This chiral ligand is widely used in asymmetric synthesis. It consists of a pair of 2-diphenylphosphinonaphthyl groups linked at the 1 and 1´ positions. This C2-symmetric framework lacks stereogenic atom, but...

 ligands and dihydrogen to reduce ketones and alkenes.

Transition metal-free catalysts, i.e. organocatalysts such as the CBS catalyst

CBS catalyst

The CBS catalyst or Corey-Bakshi-Shibata catalyst is an asymmetric catalyst derived from proline. It finds many uses in organic reactions such as the CBS reduction, Diels-Alder reactions and [3+2] cycloadditions. Proline, a naturally occurring chiral compound, is readily and cheaply available...

 based on proline

Proline

Proline is an α-amino acid, one of the twenty DNA-encoded amino acids. Its codons are CCU, CCC, CCA, and CCG. It is not an essential amino acid, which means that the human body can synthesize it. It is unique among the 20 protein-forming amino acids in that the α-amino group is secondary...

 used to ketone

Ketone

In organic chemistry, a ketone is an organic compound with the structure RCR', where R and R' can be a variety of atoms and groups of atoms. It features a carbonyl group bonded to two other carbon atoms. Many ketones are known and many are of great importance in industry and in biology...

s are known as well.