Acyclic Alkenes Asymmetric Induction
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.
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