Rare Gold-Catalyzed 4-exo-dig Cyclization for Ring Expansion of Propargylic Aziridines toward Stereoselective (Z)-Alkylidene Azetidines, via Diborylalkyl Homopropargyl Amines

Salvadó, J. Pérez-Ruiz, A. Mesas, M. M. Díaz-Requejo, P. J. Pérez and E. Fernández, Organic Letters, 2024, https://pubs.acs.org/doi/10.1021/acs.orglett.4c02415

We report an uncommon 4-exo-dig cyclization of N-tosyl homopropargyl amines, catalyzed by [AuCl(PEt3)]/AgOTf, to prepare stereoselective (Z)-2-alkylidene-1-tosylazetidine compounds. The reaction outcome contrasts with the gold-catalyzed cyclization of N-tosyl homopropargyl amines containing a methyl group at the propargylic position that provides substituted 2,3-dihydropyrroles via a 5-endo-dig mechanism. The access to N-tosyl homopropargyl amines is possible by the regioselective nucleophilic attack of α-diboryl alkylidene lithium salts to propargylic aziridines.