On Stereocontrol in Organocatalytic α-Chlorinations of Aldehydes

A comprehensive analysis of the organocatalytic α‐chlorination of aldehydes with N‐chloroimides and differ‐ ent catalysts is presented. For this reaction, alternate mechanisms were proposed that differ in the role of resting state intermediates and the rationalization of the observed enantioselectivity. This manuscript aims at resolving these funda‐ mental questions on the basis of rigorous structural characterization of intermediates (configuration and conformation), NMR studies, ion mobility‐mass spectrometry, concentration profiles, isotope studies, and DFT calculations.