Harnessing Noncovalent π-Type Interactions in Thiourea–Chloride Supramolecular Complexes: Toward the Asymmetric Dearomatization of Diazaheterocycles

Enantioselective dearomatization of diazaheterocycles through anion-binding catalysis has been developed. The process involves the nucleophilic addition of phosphorus nucleophiles to in situ generated N-benzoyliminium chlorides, using a tert-leucine-derived thiourea as an H-bond donor catalyst, thereby providing access to appealing cyclic hydrazino phosphonates and their derivatives. Mechanistic investigations suggest that the low solubility of these salts might favor the formation of a supramolecular thiourea-chloride-iminium 2:1:1 complex, which is proposed as the catalytically relevant species accounting for the observed nonlinear effect. Experimental and computational data support a 4H-activation model via this highly ordered ion pair, in which two thiourea molecules are arranged in an antiparallel orientation around the chloride, generating a C 2-symmetric groove. Hence, stereodefined insertion of the N-benzoyliminium is ensured by key noncovalent π-type interactions, thereby maximizing the enantioinduction event.