Chiral auxiliary, 14, Chart

Spatial and/or coordinative bias can be introduced into a reaction substrate by coupling it to an auxiliary or controller group, which may be achiral or chiral. The use of chiral controller groups is often used to generate enantioselectively the initial stereocenters in a multistep synthetic sequence leading to a stereochemically complex molecule. Some examples of the application of controller groups to achieve stereoselectivity are shown retrosynthetically in Chart 19. 

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