Catalytic Enantioselective Synthesis of α‐Chiral Azaheteroaryl Ethylamines by Asymmetric Protonation
2018
The direct enantioselective synthesis of chiral azaheteroaryl ethylamines from vinyl-substituted N-heterocycles and anilines is reported. A chiral phosphoric acid (CPA) catalyst promotes dearomatizing aza-Michael addition to give a prochiral exocyclic aryl enamine, which undergoes asymmetric protonation upon rearomatization. The reaction accommodates a broad range of N-heterocycles, nucleophiles, and substituents on the prochiral centre, generating the products in high enantioselectivity. DFT studies support a facile nucleophilic addition based on catalyst-induced LUMO lowering, with site-selective, rate-limiting, intramolecular asymmetric proton transfer from the ion-paired prochiral intermediate.
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