Editing Enantioselective synthesis (section)

===Chiral auxiliaries===
{{Main|Chiral auxiliary}}
A chiral auxiliary is an organic compound which couples to the starting material to form a new compound which can then undergo diastereoselective reactions via intramolecular asymmetric induction.<ref>{{cite book|last1=Roos|first1=Gregory|title=Compendium of chiral auxiliary applications.|date=2002|publisher=Acad. Press|location=San Diego, CA|isbn=978-0-12-595344-3}}</ref><ref name = "Glorius review">{{cite journal | author = Glorius, F. |author2=Gnas, Y. | title = Chiral Auxiliaries – Principles and Recent Applications | year = 2006 | journal = [[Synthesis (journal)|Synthesis]] | volume = 2006 | pages = 1899–1930 | doi = 10.1055/s-2006-942399 | issue = 12}}</ref> At the end of the reaction the auxiliary is removed, under conditions that will not cause [[racemization]] of the product.<ref name="Evans review">{{cite book |last1=Evans |first1=D. A. | last2=Helmchen | first2=G. | last3= Rüping | first3=M. | editor-first=M. |editor-last=Christmann |title=Asymmetric Synthesis – The Essentials |publisher=Wiley-VCH Verlag GmbH & Co. |year=2007 |pages=3–9 |chapter=Chiral Auxiliaries in Asymmetric Synthesis |isbn=978-3-527-31399-0}}</ref> It is typically then recovered for future use.

[[File:Auxiliary general scheme.png|center|500px]]

Chiral auxiliaries must be used in [[stoichiometric]] amounts to be effective and require additional synthetic steps to append and remove the auxiliary. However, in some cases the only available stereoselective methodology relies on chiral auxiliaries and these reactions tend to be versatile and very well-studied, allowing the most time-efficient access to enantiomerically pure products.<ref name = "Glorius review" /> Additionally, the products of auxiliary-directed reactions are [[diastereomers]], which enables their facile separation by methods such as [[column chromatography]] or crystallization.