page_title: Asymmetric induction
section_title: Acyclic alkenes asymmetric induction
hierarchical_section_title: Asymmetric induction / Acyclic alkenes asymmetric induction
caption_attribution_description: English: An example of substrate controlled addition of achiral allyl-boron to α-chiral aldehyde.
context_page_description: In stereochemistry, asymmetric induction describes the preferential formation in a chemical reaction of one enantiomer or diastereoisomer over the other as a result of the influence of a chiral feature present in the substrate, reagent, catalyst or environment. Asymmetric induction is a key element in asymmetric synthesis.
  Asymmetric induction was introduced by Hermann Emil Fischer based on his work on carbohydrates. Several types of induction exist.
  Internal asymmetric induction makes use of a chiral center bound to the reactive center through a covalent bond and remains so during the reaction. The starting material is often derived from chiral pool synthesis. In relayed asymmetric induction the chiral information is introduced in a separate step and removed again in a separate chemical reaction. Special synthons are called chiral auxiliaries. In external asymmetric induction chiral information is introduced in the transition state through a catalyst of chiral ligand. This method of asymmetric synthesis is economically most desirable.
context_section_description: Chiral acyclic alkenes also show diastereoselectivity upon reactions such as epoxidation and enolate alkylation. The substituents around the alkene can favour the approach of the electrophile from one or the other face of the molecule. This is the basis of the Houk's model, based on theoretical work by Kendall Houk, which predicts that the selectivity is stronger for cis than for trans double bonds.
  In the example shown, the cis alkene assumes the shown conformation to minimize steric clash between RS and the methyl group. The approach of the electrophile preferentially occurs from the same side of the medium group (RM) rather than the large group (RL), mainly producing the shown diastereoisomer. Since for a trans alkene the steric hindrance between RS and the H group is not as large as for the cis case, the selectivity is much lower.
caption: An example of substrate controlled addition of achiral allyl-boron to α-chiral aldehyde.
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