Chapter 7 - Ionic reactions 2: Diastereoselectivity and asymmetric synthesis

Abstract

This chapter describes diastereoselectivity and asymmetric synthesis involving ionic reactions. Diastereoselective carbonyl additions are described using Felkin–Anh, polar Felkin–Anh and Cram chelate models, and also by Prelog’s rule. Diastereoselective Narasaka–Prasad and Evans–Saksena reductions are included. Asymmetric carbonyl reductions with chiral borane and chiral hydride reagents are provided. Asymmetric deprotonation is included. Catalytic asymmetric dialkylzinc addition and CBS reduction are described. Diastereoselective lithium and boron enolate formation is explained mechanistically. Asymmetric enolate alkylations are described using several chiral auxiliary approaches, Seebach method of self-regeneration of chirality and asymmetric phase transfer catalysis. Diastereoselective aldol reactions based on Zimmerman–Traxler model and several asymmetric methodologies for aldol reactions are described. Asymmetric Brown and Roush allylations, and asymmetric Ellman synthesis of amines are included. Diastereoselective alkene additions are illustrated using Houk models. Asymmetric hydroboration and Shi asymmetric epoxidation are described. Asymmetric methods including organocatalysis for conjugate additions are presented. Some enzyme-catalysed reactions are also included.