Enantioselective Intramolecular α‐Arylation of Benzylamine Derivatives: Synthesis of a Precursor to Levocetirizine

Abstract

A practical, transition metal‐free method allows the enantioselective synthesis of α,α‐diarylmethylamines by asymmetric α‐arylation of benzylamines. Enantioselective lithiation of N′‐aryl‐N‐benzyl‐N‐isopropyl ureas using a chiral lithium amide base generates a benzyllithium that undergoes an unactivated stereospecific intramolecular nucleophilic aromatic substitution to generate an α,α‐diarylmethylamine in the form of its urea derivative, in up to >99 % ee. Treatment with acid induces an “azatropic shift” with retention of configuration, the product of which may be hydrolysed to the target amine.