Diastereoselective N-quaternization of piperidines

The study of the N-quaternization of substituted piperidines has been mostly dormant for the last 40 years, despite the demand for ammonium salts as drugs, ionic liquids, chiral catalysts or ligands, phase transfer reagents, and reagents for the Stevens and Sommelet-Hauser rearrangements. In this perspective article, the complexity of this seemingly simple reaction is studied by a summary and analysis of literature experimental results. Computational methods are applied to various literature reactions as case studies.